5 piece doesn't promote creativity any less than 4 piece - just think of it as a 4-piece, plus an auxillary drum.
I feel like more drums is better suited to pre-written music, requiring more delicate orchestration. Less drums can facilitate more spontaneous, ad lib playing. I'd like to have the options of a larger kit, but only play or bring the drums required by the music. Like a shell bank.
Again I think it just boils down to what a player considers their home base - their basic tool kit.
Lots of guys are at home base with a 4 piece - and see that tom as something added.
While others, like myself, sit at a 4 piece and feel like I'm sitting at a kit missing a piece.... like opening my toolbox and finding I have brought a crescent wrench. Now the job at hand may not need a crescent wrench, but it just makes me uncomfortable knowing that it's not there, if I need it.
And personally I play both a lot of scored, written music as well as lots totally ad lib stuff (pop, rock, but also weird jazz, etc) - and it's easier for me to play both on a 5 piece - for no other reason, than that is what I'm most comfortable sitting behind. It is there that I either most able to close my eyes and play... or glue my eyes to a chart - while knowing that everything is right where I'm used to it being.
This "home base" doesn't seem to be a big deal for some players... but others it seems like it may be. I can't help noticing the number of players that play in a wide variety of styles and settings - settings that would suggest setting up different kits for each different settings - that stick with the same basic set-up from gig to gig - no matter how different gig maybe. Gadd and Vinnie most prominently come to mind. They seem to have "their instrument", configured how they are used to - that they then go out and play all sorts of different gigs with.
All boiling down to basically... there are no rules with this... it is pretty much, simply... what ever works.