I started with soft15kHz, then switched CRT_Emudriver, and I would never go back. Ultimately, you are achieving the same thing with either one, in one terms of the resolutions you are able to display, but setting these resolutions up is sooooo much more cumbersome in Soft15kHz using Powerstrip than it is in CRT_Emudriver using ArcadeOSD. Furthermore, with Soft15kHz you may be limited in how many different resolutions you can use, which can become a problem with the multitude needed for all the different games in MAME, whereas the "on-the-fly" auto-generated resolutions of CRT_Emudriver + GroovyMAME basically give you an infinite amount of them, while also saving you the trouble of setting each one up yourself. If auto-generation is not your thing and you really want total control, there is going to be an update for GroovyMAME which will allow you to use your own custom modelines "on-the-fly" by stating them in a game's ini file, which I am really looking forward to.
As far as a video card goes, that shouldn't be an issue. You can get a Radeon HD4350 (what I'm using, highly recommended) on eBay for about $20.
GroovyMAME has a lot of other unique and powerful features which make it worthwhile as well.