As Dan said, there's far-better (and less-confusing) exposure as separate ads.
Makes loading ad pages easier (not filled with a shedload of pics).
Makes it less-confusing / more-convenient to be able to scan what's available as thread titles than to be left wondering what might be in a smorgasbord ad.
The only downside I see is the issue of bumping them all at-once. I've spoken at length with complainants and "perpetrators", imploring the latter to bump their glut of ads tastefully. That is, not 20 at a time, but rather limiting it to 4 or 5. That way 20 other peeps won't suddenly feel like they have to bump theirs after being moved off the first page. Even worse, someone might have only just bumped to page 1 and then he gets hit with the 20-at-once-thing and has to wait another 24h (it's the rule) before another attempt to gain some exposure.
IOW, it's all-good but if you see someone bumping a page's worth of ads at the same time, feel free to either point it out in one of the ads or let me know and I'll deal with it.
I totally get how it feels when this happens and have thus far done everything I can to address the issue when it arises, which isn't often. Just remember: If it does occur, it's not in the spirit of community and can be justifiably called-out.
HTH