Worth mentioning that ADS-B uses GPS position reports (GPS itself must be certified, I think that panel installations of 296/496 wouldn't be allowed for ADS-B), not anything else based on self-sustaining navigation tools such as INS/IRS or radio-navigation based such as DME/DME or VOR/DME.
I think that given that the majority of VFR traffic is still not equipped with Mode S transponders (let alone ADS-B), the best thing you can currently buy is PCAS (Portable Collision Avoidance System) - it doesn't have graphical presentation, but I think the direction, altitude (relative or absolute) and vertical speed (well, indication of climb, cruise or level flight) is more than enough information to avoid any VFR traffic you don't have visual contact with.
I think the main problem with using ADS-B as a means of avoiding collision is that only large transport aircraft have it - and as it was mentioned, smaller regionals such as CRJ, ERJ don't, so you would be effectively protecting yourself only from A320, B737 or larger. Not quite the protection I'd want. I would also like to point out that the most dangerous operation (regarding posibility of mid-air collision) is VFR-VFR outside controlled airspace, since you have many non-transponding aircraft, which are flying low, many times below radar coverage (so FIS can't give you traffic information), many times there is a really poor lookout for other traffic, etc. What I'm not worried about is possibility of IFR-IFR or VFR-IFR collision in medium-busy controlled airspace, since most IFR traffic has MTOM over 5700kg and thus requires TCAS on board, and even if you don't know you are on a collision course, they will and they will avoid you.
I have to say that over-reliance on TCAS could be a problem, but is usually present with airline pilots. I've heard quite a few times at the airport I usually fly from that airliners are reporting TCAS TA/RAs to ATC regarding VFR traffic flying traffic patterns. All good and well if it wasn't the usual traffic pattern (obviously not as wide as an A320 would fly) and flight visibility was 50+ km. So all in all, I think the most important way to avoid collision is good lookout and when that's not available (IMC or otherwise poor flight visibility, such as flying directly into sun), one should begin relying on TCAS/PCAS.