Are there any political reasons why Russia could attack Poland or threaten to attack?
And another thing, would placing a NATO base in Poland might be received as a threat to Russia?
Usually when country A declare war to country B, it is for one of the following reasons:
About natural resources
Russia already has an amazing pool of natural resources. Poland's resources are made mostly of coal and agricultural products. Russia already has plenty of coal and agriculture thus it won't attack Poland for its natural resources.
Russia has effectively been at war with Poland many times, has participated to the partitions of Poland. Since then poles got their revenge in 1921, and USSR got its revenge again in 1939, which was confirmed in 1945 at Yalta conference when the allies decided to give the eastern half of Poland to USSR.
The newly annexed territories are effectively smaller than the former Russian partition of Poland. Technically, the regions of Bialystok, Warsaw, Lublin and Lodz had been Russian at some point in recent History and could technically be claimed by Russia.
However USSR had the last word in Polish-Russian territory conflict, so there is really no chance of Russia wanting revenge, if anything, it would be Poland which would be a potential threat to its eastern neighbours, would it want get back its former pre-1939 eastern territories.
About ethnic minorities
Poland had been violently ethnically cleansed between 1939 and 1950, so that its Jewish, White-Russian, Lithuanian, German and Ukrainian minorities were either assassinated, expelled or left by themselves (or a combination thereof). Poland is today the most ethnically homogeneous state of the European Union, having close to 97% of the country's population being Poles by blood. Although a few groups managed to hide and survive the various ethnic cleaning and stayed in Poland, there is not solid claim for Russia to protect a Russian minority in Poland. If anything, it's Latvia and Estonia which have something to fear of in this respect (and Ukraine obviously).
Nevertheless it would be a bit early to conclude that Russia is not a threat for Poland. First, even though Poland is part of NATO, history has shown in 1938 and 1939 that western allies are not very prompt to defend their central European allies when attacked. Should an eastern NATO member be attacked by Russia, it would not be surprising to have another Phoney War happening.
Russia could also be an indirect threat to Poland through Belarus and/or Ukraine. Belarus has very close relationships with Russia, and is a crazy dictatorship. There is a lot of chances that someday people will revolt again the regime, creating a civil war climate, similar to what happens in Ukraine nowadays. In that case many refugees will chose to go to Poland because of their geographical and cultural proximity. The same could be said if Russia would take more offensives against Ukraine.
The Kaliningrad enclave question is still open. It is the only place where Russia borders directly Poland, and is one of the most densely militarized part of the world. Both Russia and NATO considers this place being dangerous because of the proximity of the other. This place has been historically German, and before that Polish (not in the sense it was populated by Poles, but that controlled by the Polish state). Who knows how this question will evolve.
Finally, Poland and Russia had been historical enemies for a very, very long time, and there is much resentment on both sides. Russia is still denying that the USSR was a rogue state (unlike Germany which fully admit their former wrongdoings), and while they admit some of their crimes they try to pass them as the doing of wrong individuals into a right state, instead of admitting how terrible the USSR was under Stalin, and that it was more the rival and twin brother of Nazi Germany rather than their enemies fighting for the good they think they were. The supposedly accidental plane crash of April 10th 2010, in which many high ranked polish politicians perished is very fishy, and is suspected to have been a terrorist act from Russia against Poland.
Although Russia is not a direct threat for Poland, it could be an indirect threat through Belarus and Ukraine and the Baltic states if Russia starts bothering them too much, as refugees would naturally seek refuge in Poland. Also, Polish-Russian relations have been and continue to be poisonous.
There's a lot of talk about Poland and increasing forces and greater Nato presence there, but I don't think Russia is a threat to Poland cause I don't think Poland is a threat to Russia. That doesn't mean things couldn't get heated and some trouble can't happen, but I don't think it's a particularly hot spot, though certainly the 2nd part of your question has some truth to it. Growing Nato bases in Poland wouldn't sit well with the Russians.
Crimea (and Georgia a few years earlier) were different for 2 reasons. They had more strategic military benefit and both those regions had high Russian sympathetic populations. Poland doesn't (as far as I know) have a high population of Russian sympathetic citizens. Poland is a also member of Nato and a member of the EU. I have a hard time seeing Russia taking that on, though, you never know, I suppose. Putin's crazy.
Poland in a natural enemy to Russia, because they interests collide in eastern Europe. Poland attempts to build a block of countries in central and eastern Europe that with support of USA would balance the influence of demographically stronger Russia and Germany in the region. Especially every attempt to take Ukraine and Belarus out of Russian sphere of interest would meet hostility in Russia.
From Russian perspective Ukraine and Belarus are part of greater Russia, while Poland should be a buffer between them and Germany. Russia will always attempt to destabilize Poland to make sure she will not be able to project any influence in the region.
Poland is also the only way NATO could support the Baltic countries. Without Polish territory there is no way anyone would save the Balts from Russian troops. There is a big Russian community there, so Russia will try to control those countries.
During the cold war Poland was a crashing zone between NATO and Soviet Union. In case of war the NATO forces were supposed to be stopped there before reaching soviet territories. Let's remember that Soviet Union made a deal with Nazi Germany to participate Poland. Perhaps those few hundred kilometers they gained stopped Wehrmacht from reaching Moscow. Russia cannot afford to have hostile troops too close to their borders. Ukraine is too close, Poland is 'close'.
Russia would try to weaken Poland, but full scale invasion is not very likely in near future. A small war at the border to cripple Poland, gain control of the Baltic states and isolate Ukraine from the west is not impossible. Russia is getting weaker every year, but still have a big army. Maybe they will try to use it, when they can still afford it.