At the simplest level, the 472 is a dual band 978 MHz (UAT)and 1090 MHz ADS-B receiver, while the 470 is only 978 MHz. Since aircraft have the option to equip with an emitter on either frequency, it lets you see more ADS-B equipped aircraft directly when you're in line of sight of them. However, that's not the whole story. Most US aircraft aren't equipped with ADS-B Out yet, and although that'll change, no ADS-B receiver can directly see aircraft that aren't equipped with an ADS-B Out device. Even once 2020 comes around, there will be many many aircraft that choose not to equip, and neither the 470, 472, or any other ADS-B receiver can see those aircraft directly.
BUT, the designers of the ADS-B system saw this problem, and also needed a way to beam up weather information to aircraft. So the network of ADS-B ground stations actually collect all of the aircraft in the vicinity of ADS-B Out emitters, and send you back a nice package of info that includes the "full" traffic portrait, including targets that are only being picked up by a terminal or regional FAA radar. The net effect is that when you're in coverage of a ground station AND are an ADS-B Out emmiter (ie equipped with our SV-XPNDR-261, and after 2020 the SV-GPS-2020 for compliance), you basically get all of the aircraft whether your receiver is dual band or single band.
If you're not in range of a ground station, which is most likely to happen when you're low to the ground or in a very mountainous region, then a dual band receiver is theoretically better than a single band receiver. But then you're right back up against the fact that there are a LOT of aircraft that aren't ADS-B Out equipped, and you won't see them period. So to compare, with ADS-B ground station coverage, you'll see 100% of aircraft that the FAA can see. Let's invent some numbers and say that 30% of aircraft in a particular area are ADS-B Out equipped (today, this is actually generous). Let's further assume that of those, 70% of them are 1090 equipped and 30% are 978. That's a random guess and might be very wrong, but in the aftermarket transponder (1090) based solutions look to be more popular than 978 versions, although recent product introductions may shift that over the next view years. So outside of ADS-B ground station coverage, if you have a 470, when you stack up the above numbers, you'll be able to see 21% of the aircraft around you in this scenario. If you have a dual band receiver, that goes up to only 30%. Both of those are rather incomplete traffic pictures. Once you emerge into ADS-B ground station coverage, that number goes way up if you're in a radar coverage zone. And even if you're not, the aggregation of all of the ADS-B targets alone gets you that higher 30% of traffic regarless of whether your receiver is single or dual band.
Anyway, the overall point is that being in range of a ground station AND being in radar coverage is when ADS-B traffic works best. Any other time, you're missing out on a lot. And the difference between single and dual band receivers with in today's equippage rates isn't all that much.