How tight are resources in Game Mode+, do I need to exercise restraint with using medikits and grenades or is there enough to go around as in normal mode, and did you have any credits left after finishing Game Mode+?

I just started to replay the game in this mode and it's very enjoyable, definitely more challenging. However, I already had to use one grenade very early into the campaign (when the aliens bum rush your base after you find Sam) and it wasn't even against armored enemies so I'm wondering how generously or not I can use what I find. Grenades are expensive and sparse even in normal mode and I'm expecting to need a lot more grenades in game mode+ so if you have any strategic resource management tips for this mode, I'd very much appreciate it. Thanks!

Just finished the campaign in game mode+ and it was a lot of fun. No problem with running out of resources.

At one point, I had 5700 extra energy credits so there is no need to worry about running low. Before the final mission, I still had plenty of energy so I went ahead and bought a lot of medikits and ammo and filled up my inventory, and still had more than 2000 credits left. When I finally beat the last mission, my inventories were still full to the brim and no one in my team died so it appears I was worried for no reason. Game mode+ is challenging but not unfair or cheap.

In general, I could have used more grenades and medikits instead of being ultra conservative with everything. I also didn't use up many stimpacks until the very end because I wanted to be able to distribute them in a way that everyone has at least 6 AGI and 8 AIM (except for Thirteen who only had 5 AGI while wearing the Tank Prototype, and no points in AIM because he used the chainsaw gun). Not using most up my stimpacks as I went along made the experience considerably harder, especially Lab 27B which is the number one hardest part in game mode+.

Is there anything new in GM+?

No, there aren't any new missions, items or enemies.

You get a larger number of enemies (in some cases up to twice as many) and they're considerably tougher and deal more damage, all in all it feels about twice as tough but if you've figured out how the AI moves, it's not a big problem as long as you're careful and don't try to take shots with low hit chance all the time. Position and cover are now absolutely key because you can die a lot quicker in game mode+. There was only one level where I got massacred down to the last character, that was a close call.
Other than that slaughterfest it can be solved with tactics, luck doesn't factor in really. I almost felt game mode+ was harder in the beginning and middle and became easier towards the end once you get good armors and shields, in normal mode the levels get harder towards the end.
I recommend game mode+ because it forces the player to really take advantage of cover and not let anyone (who isn't Thirteen w/ Tank Prototype) stand out in the open. In normal mode, the game can get a little bit dull in the middle but in game mode+ it's a fun challenge throughout.

The Cryo Prison and Lab 27 levels are a trip, felt like Alien 2 the movie with a bit of this scenefrom The Rock thrown in.