Reclaim values are high, and raiding one's base is risky because of that, i agree with that. Too often you kill few t2 mexes with a t2 arty drop and it doesn't even matter cause the wreck is ~750 mass, and you gave 12 t1 arty worth of reclaim to help rebuilding them.
However i don't think the game is that inbalanced in favor of t3 mexes.
Canis, dual gap, open wonder ... etc are maps designed to end in a stalemate very quickly, and where it's very hard (because of the map's design) to counter ecowhoring. Increasing cost/time of mex upgrade might allow more possibility to crush the stalemate at t1/t2 stage, but i don't think it'll solve the "problem". Getting eco upgrades will still likely be the best strategy just due to map's design.
I'm not a pro at seton's gameplay, but i've seen many games where one team just go all in with t2 drops/t2 air and just crushes opponents who just invest in t3 mexes. On a lot of map (tmm maps included), i think there's often the possibility to bypass the main front with t2 transport, or to raid with air, and make the game messy. I would agree that it is not a very popular move, people tend to prefer staying safe rather than investing into aggression. Same can be said about firebases and static gameplay. People tend to fall back and eco when they see their opponent turtling, rather than investing into ACU upgrades/MML/T2-T3 units to break the stalemate.
I truely feel the game is quite balanced regarding the cost of t3 mexes, the price of t2 aggressive units (T2 transport is quite easy to make, MML are cheap and strong, T2 aggression is generally strong and efficient ...).
The fact that a lot of players like eco-whoring maps, and always play very stalematy maps for teamgames instead of more open ones ... i think you cannot change that with tweaks on cost values