N's are actually worth 50 experience points each
R's are 100
SR's are 200
SSR's are 400
Matching elements multiply the exp by 1.5
Leveling the material would increase how much exp it gives, but it's not linear. There's a table on the wiki if you're curious.
The 50% bonus from matching element kicks in afterwards. So let's say you leveled up an R to lv 15. Lv 15 adds 40 exp, so now that accessory offers (100+40)=140 exp. Matching elements would multiply 140 by 1.5 to get 210.
There will also be rosaries, which are specifically meant to be exp fodder. The R rosary gives 150 and the SR rosary gives 300 exp. They're phantom/illusion element, so I assume no matching bonus for them.
N being worth 10 is actually for accessory points for the exchange; nothing to do with leveling.