There are third party boards for both PB and PL that add quite a few maps. Extra maps also exist for AIW/Desert. There is new terrain and additional level above the usual flat hilltop. The desert boards allow for escarpments and dunes, etc. Unfortunately the desert boards use too many village hexes with inferior graphics (which could simply be ignored, I suppose)
For PB -
http://www.imaginative-strategist.layfigures.com/IMSTRAT PB Maps.html
For PL -
http://www.imaginative-strategist.layfigures.com/IMSTRAT PL Land.html
For AIW and WWII Desert -
http://www.imaginative-strategist.layfigures.com/IMSTRAT PL Desert.html
These websites also have variants for the entire war as well as links to a second developer who used more up to date information for variants from the original designer. The improvements are minor overall but he left some original PB/PL units as they were because they were "canon". He didn't fix the issue with infantry firepower.
The problem with the system was not so much terrain or the armour but the infantry. The values were based on AT ability and not infantry firepower
and AT ability. There probably should have been tow values for infantry. Thus you have German rifle platoons "out shooting" US infantry platoons, which, considering the amount of lead a US platoon could put down range, was a definite flaw. Allied MG platoons were also woefully under -gunned.
The capabilities of the Russian armour and infantry were also very much "cold war" views that were biased towards the "hoards of bodies and avalanche of steel" view that has only been corrected in the last 10-15 years.
They did fix the problems with artillery in AIW which translated well into PB/PL. You could no longer weaken an artillery attack by stacking the hex to maximum (more density). They also fixed the speed issue (tracked vehicles were rated for max road speed) slowing down the tanks.