It is true that holy priests have more difficulty killing things. The other day Dpre asked for help with the dailies for that very reason - you should not be shy about doing the same thing if you decide to switch.
As a holy priest, I think you will have lots of opportunities to join groups, and that would need to be your focus, since healers don't solo very well. Of course your brother and you would make a formidable two-some. Arv has a friend, Oosill, a shammy healer, and they met in their thirties. We ran with Oosill the other day, and he had all dropped epic gear - every slot, whereas Arv has only a few. The reason for the descrepancy? Healers can go to any instance anytime they want, pretty much.
If you're on alone and are not having fun soloing because you have trouble killing things, then work on your alt. Your attitude about what your character is for has to be switched just as much as its spec.
You should not switch just because it's good for the guild, but because it's what you want to do. Some people really enjoy healing. If you find that you don't, you can always respec back again. It's only money. I'm selfish - I want you to respec because it's good for me. It will be more likely that I can join/create a group - a complete group - with people I enjoy running with. You should not feel pressured though, you have to live with the decision.
Good luck, and let me know if I can help with your dailies anytime.