Perhaps my serger is different (it's incredibly old and weighs a ton) but I find the serged seams way easier to rip out. I can just run my seam ripper down the horizontal threads and the seams pull apart, rather than my machine with a straight stitch where I had to go every few inches and rip more little threads. I used my machine with a straight stitch for the bodysuit and will use it for the bodice too, there's just a lot of room for small errors in the skirt due to the nature of the cut, not to mention they're pretty much just straight seams and pretty simple to sew.
I am by no means an expert on any of this by the way, I'm just sharing my experience so I welcome the wisdom of more experienced dress makers.
I've been thinking more and I think I'm going to have to break down and put in a zipper to get the right fit. ::sigh:: I didn't want to put in a zipper because I always find zippers to be prone to failure, plus it's a pain to actually sew one in.