There is still a res "cap". You should never get near it. It is true that having more than 1200 res in kind of pointless. At the time that you have 1200 res, as a priest what needs to be in your mind is more along the lines of "how can my partner(s) survive." If you have 1200 res but your partner gets killed every time (especially since DPS do not often get a lot of res) then it does not matter. Once you are over 1k or maybe even 1.1k then it is time to look at your other stats. You are a healer, you need to function as one or you are not doing your part on the team.
Increasing your stats that help you heal also increases your survival so it is not like you are giving up survival for better healing. Better healing is better survival. Some priests I have seen have the problem of thinking along the lines of "I die too much, I must not have enough HP/Res” This is not always the case. It could be that your spell power is not high enough to counter Inc damage. If a dps get more atk power to do more damage than after you reach a good HP/Res you need to increase your spell power to Inc healing to counter their Inc in damage. Haste gives you faster heals, crit gives you some more random burst healing, and spell power gives you a flat Inc.
In my opinion you should have all at a balance. What that balance is can be argued because there is no correct answer. Some players do not need the haste. At all. They get 2600+ without it. This is not just due to them, but their partners and their team play style. Some teams do amazing with haste and use it to its full potential. They are also at 2600+ and have play styles that make the most of the haste.
This debate about best stats after you obtain the base of the mains stats is not something I want to get into on this thread as it is an endgame topic and this is a starting out thread. There are tons of discussions on AJ though.