I feel that the concept behind carrying your media on a single(or at least backed-up) single large format media(such as a BIG hard drive) is a wise move. After all, especially since YOU, as a DJ, might have a clue as to what the people want at a gig, might run into the reality that what you thought people wanted was NOT what they really wanted.
For example, the trash music genre known as "hip hop". I won't go into why it's trash, but it is, because it's too big to flush. But at any rate, let's say you bring hip hop, and your client is not really into it.... Man, are you screwed! Maybe they wanted oldies for example, because they are geriatric or whatever. At any rate, having a lot to easily fallback onto will be a big bonus.
32gigs of full 16-bit 44.1K PCM audio is a LOT of stuff to carry around on one compact media. I suppose your best bet is to sort into categories and then stuff onto sticks and cards, and label with a Sharpie(and then cover that mark with packing tape so it won't rub off). Then a card of what you're finding to be "most requested stuff".
You are right about club owners: They don't want to invest anything into anything outside of booze. Most clubs around here are in two categories: crappy and "clean". Even so, the clean ones don't want to invest, but the crap ones are just falling apart. I mean that literally, sadly enough. DJ booths reeking of pot, unine and cigarette smoke, gear gummed up to the point of catastrophic failure(that's why it failed and burned up), and then they want me to come in and pull a miracle out of my butt to make it all happen. Total budget for total system overhaul: $5 in booze(and I don't drink). That's what club owners expect.
Since I don't do the DJ thing, I don't have to deal with those issues. I tell people "go tell the band what you want to hear, because I'm just mixing and no, I'm not with the band". Still, 400 songs on average for those hard to find 32GIG cards and sticks is a lot to deal with. I can do 4-6 hours on a 4GIG, but that doesn't give me a lot of variety should it need to be mixed up. That amount works fine on my iPhone since I'm playing for me.
I'm sure soon, internal hard drives will be standard, using some sort of common platform format that can be accessed via Mac or PC and a USB port. I say less than 5 years. Hard drive prices have to come down more in the 1-2 Terrabyte catagory, as well as improved reliability, lower heat. I recently had a Seagate Extreme overheat(1.5 Terrabyte) and fail because the case design is pure crap.