Very good question since GoPro shrewdly do not offer a direct comparison between old and new models. Similarly on youtube, etc., all reveiws/comparisons are between Black+ vs Silver+, not Black vs Silver+.
While GoPro do list product comparisons for their latest products, they don't compare older versions. They also make statements like 'Boasting 2x the performance of its predecessor,' which could be referring to the 'standard' edition...
I think the best think to do is find a detailed review of the Black+ and note the changes from this to the Black standard. Then do the same for the Silver+. Then you can work out what changes will be important to you.
The main change to the Black/Silver+ editions seems to be the inclusion of a better battery (more capacity). It also is supposed to have better WiFi, sharper imaging (compared to the 'standard').
Tech specs that matter such as frame rates, etc., do not seem to be changed. So if you want the best 'camera', with higher quality camera settings (for example) the Black would most probably be better. If you want the best 'GoPro' experience, then it might be worth going for the Silver+.
You can always invest in a spare battery and for a day out shooting - you'd need one anyway, even if the battery life is 20% better than it's 'predecessor'.
They will most probably release a Hero4 at some point soonish, so I'd go for the best tech spec for the price, rather than best WiFi settings, etc.
I hope that helps.