Planetary Fortress upgrades

So, I was playing Squadron tower defense and it came in my mind why doesnt Desert strike have possibilities to upgrade Planetary fortress? I didnt thought too much about pros and cons because IMO its best to discuss about those here with more people. But for start it will definetly make games longer which I like and I think many other will agree with this. Its just not fun to win/lose before even second area opens.

Upgrades could be damage, more hp, faster regen and more armor. Thats pretty basic. But what I really thought is that we only add damage, HP and armor and leave Planetary Fortress without regeneration. What I can see with this, is that when you finally get to opponent team's Fortress with biggish army, you wont one shot the Fortress, you have to do this same at least 2-3 times before you win. If you have played Starjeweled, you know what I mean.

Well, it will drastically increase lenght of game if done without regeneration and replaces with loads of more hp, but I think it wont make Desert Strike worse if it would get upgradeable Planetary Fortress, even with regeneration.

What you think? Feel free to add your modifications to this etc.


EDIT: I forgot to mention that if this could be implemented, of course planetary fortress (and cannon) would be alot worse from start than they are now. Like if Planetary fortress is doing now 70 dmg always, it could start from 20-30 and you could upgrade it to XXX as the game goes on.

IMO there are several reasons why this is an idea that is hard to implement (from design perspective):
- Why would i want to upgrade defense, if that means weakening my offense (less money on troops)?
- Can one player upgrade it for all players? (defense buildings are shared)
- Should losing players make the game longer by upgrading defense, therefore ensuring their loss (spend money on this instead of attack, never gaining middle ground bonus), but making the game drag on longer for no reason?