I recently had an encounter-game where it was a clutch situation and I went to the cap. I was at 97 points when I got spotted and the arty killed me. The arty got a Defender medal for that, but I didn't get anything ( It didn't even show capture points in the post game stats since the cap wasn't succesful). Even if the cap had finished, I don't think I would have gotten a lot of experience for it. The arty on the other hand only had to splash anywhere near me to get a shitload of XP and the "defender" medal.
Also I have the feeling that the cap circles are often carelessly placed completly in the open without cover so noone even bothers with it since they don't get much back for taking the risk – and I have seen a lot of games being thrown by greeding for the last tanks.
I think capping isn't rewarded enough and should be reworked.