there is one glaring difference other than gui. that is placement of custom modifers on the map. you can edit tiles.dat and add more modifers, but in lite you can't actually put them on your map. you can edit the 4 custom modifiers that come with lite, but you don't have the gui to do it "right"
**ok apparently the 4 default "column" modifiers that come in tiles.dat are not available in free version to be placed on the map, so you can't even do what i said above.
virtually everything else can be done without using the gui editors that are part of pro.
with that said, i don't think a level playing field is all that important in the grand scheme of things. you can make good games with lite restrictions, you can make the same game in pro the only difference would be custom modifiers that change the shape of the square "tiles"
it's only $10 usd. it is well worth that and more. i payed 20 for mine just to support the dev. (he used it to buy vodka)
pro users do have an advantage, but it is not an "unfair" advantage. if you want your game to benefit from the pro features, cough up the cost of a meal at mcdonalds. if you don't want to do that, use lite and be happy with your decision.