I had a Bolt and moved to a 530 last fall (so some of this info may be outdated with the new Bolt and any firmware updates).
Setting up the screens on the Bolt is easier/more intuitive, that's the major selling point that it has over the 530, IMO. Once you're beyond the set-up stage, though, I don't think that there's really an ease of use advantage.
I like the maps/nav on the 530 is better. The screen is more legible. TBT cues are available on courses created on platforms other than RidewithGPS, which is the only way that I could get TBT to work on the Bolt. Also, audible TBT cues if you have BT headphones/speaker. I also like the fact that you can bring up the map screen and it'll tell you which cross-street is coming up next, even if you don't have a course loaded, so if you're not completely familiar with an area, but you know that you want to turn on County Road 26 or whatever, this feature helps. I know that you said that you don't use nav that often, I didn't either, but the usability of maps on the 530 resulted in me creating more courses and exploring more.
The 530 also has ANT+ light control, which the Bolt didn't have. It's not a huge deal, but it does give you a couple nice features: 1) you never have to fiddle with the single button on the Varia anymore - you start your ride on the 530 and it fires up the light. 2) you have the option of running the radar without a light, not something that you can do without ANT+ Light control.
Oh, btw, the 530 isn't touch screen - that's the 830.