Sorry it took so long to reply, I just got done moving... Anyway...
@SlimJim: the towers go red to advise you that you do not have enough resources to produce the units of that tower any longer. There is not a unit limit per tower per say, however for each unit that is alive from that tower the cost of the next unit goes up a bit. I made the tower go red so that you know you don't have enough resources to produce any longer, and to help you remember/notice this, and put that tower into collection mode.
@adamkad1: For a while I did have the coins auto generate, but I liked this solution better. If more people are interested in auto coins I will come up with a new coin generation system.
@infernoblade can you elaborate a little with the zoom fail? I found the problem with the frame rate crash with multiple towers, It should be up later tonight or early tomorrow.
@SlimJim7977 Good suggestions, I will change the color of the units, I am working on an update already from the notes today, one of which will be to limit the number of units a tower can create.
@keith075: I updated the description, personally I would not rely on one tower, and when I play I make a tower every chance I get. There is no other use for coins yet so expand =)
Must not have been clear, the stats on the tower are the stats of the units, so as you upgrade the agility on your tower you are actually upgrading the agility of the units.
 "Tower On Tower Action"){kind=icon}
 "MegaDrill"){kind=icon}