Forget swapping the spring even in an ICS...just contact Shinobii and buy an second complete upper. Keep one for indoor (300-330ish) and drop a spring into the other for outdoor (380-sub400).
Then swapping back and forth between indoor and outdoor games takes about 30seconds...and if your upper fails at an outdoor game, you've at least got a backup to finish out the day.
If I had to choose between a clear/tinted G&G and a clear/tinted ICS...I'd choose an ICS, hands down.
I can build/tune pretty much anything I want...but with all the repairs and stuff, I hardly get to work on my own stuff. Being able to slap in an indoor upper and shoot a CQB game friday night...then slap an outdoor upper in for a field game the next day...that'd be awesome.
And for durability...the tough (but brittle) polycarbonate that G&G's receivers are made of...that sucks for a lower receiver. The plastic of the ICS is different...it'll flex where the G&G receiver will break.
Just my $0.02