I don't think any Gallery art is tied to Abyss. It's just Abyss is the fastest way to earn P$ so you unlock it. Unlimited, and AI Level Down are the best ones to buy imo for runs. Read this guide: http://www.ps3trophies.org/forum/blazblue-continuum-shift-extend/141205-blazblue-continuum-shift-extend-trophy-guide-road-map.html
I personally spent a month doing Abyss runs just to 100% it's item list. On average I see it takes people a week or two.