Definitely am.
Maybe there are better ones I should be using? I'm mainly using Bill with Bill's Spirit and two extra hit points, the latter of which are probably why I keep making it to the end by the skin of my teeth.
Overloads, a little less so. I try to use them before I lose my last bit of health, but I'm not always successful.
I do when I can/need to, all the way back to Contra III. At the start of this level, it doesn't seem to help, though, as the guys down below seem to be moving just out of range.
In fact, it seems like staying still for too long most of the time invites trouble... this stage is BUSY.
But I definitely use it where I can. Particularly on Gordea when he's doing his thing on top of the trains.
...uh, does shooting him there count towards when he comes down to fight you? Or am I just wasting my time trying to get extra hits in?