Two Questions

First of all, is it worth it to work on getting sunspear points after rank 7? I know earlier on it gives you more quests, but will it still give more quests at rank 8, 9 and 10?

My second question is about hard mode, how come in some area's it counts your kills, but not in others? Is there something special if you get to a certain number?

if you get to a certain number (the number of mobs in the zone) then you get a point towards your vanquisher title.

as for sunspear rank, higher levels make the signet work better, and ANet is going to be putting in more skills for the different levels of the title in the near future.

I don't think there will be more quests, but soon there will be new Sunspear skills coming out, so it probably will be beneficial to have higher ranks.

Not all areas count for the vanquisher title. The RoT area in Nightfall doesn't count, for example. Once you completely clear an area of every enemy AI (the number in any area varies somewhat depending on active quests, pop-ups encountered, etc.), you'll get a gold reward of 3x the number of enemies killed, and an XP reward as well.