What are your opinions on when to change the thermal pads and paste on a card? This is my first very high end card and i would like to keep it running for many years to come, any advice would be really helpful. 
 
EVGA 780 Ti SC ACX
 

Many years to come? Forget about it. :)
You need not do anything with paste and pads. Be sure to regularly blow dust out of fan and heatsink though.

I wish to ask Scarlet-Tech what issues he has had with his 780 Ti Classifieds and it's paste? I suppose if you are folding 24/7 you may wish to change your TIM in a year or so but for someone putting a daily few hour load on them I see no need to change out the paste. These 780 chips run so cool it's a Godsend. I had two 470's in SLI for several years and those babies were egg fryers. I think I changed out the TIM once, at most twice. Unless you are seeing idle temps of 50 degrees or higher I'd say don't worry about it. Just make sure you give them a good dust off when you do your regular maintenance, like every month or so is my schedule. Most TIM's of reputable manufacture are made to last upwards of 7 years before drying out.

I have a thread where I change the TIM on 3 different lines of 700 series cards, (750ti, 760, and 780ti Classifieds). You can search for it and see the glob of thermal material they put on all 3 lines. It is twice the size of the die and quite messy. The 750ti had way more than necessary, and even though the card ran at extremely low temps, changing the TIM reduced the overall max temperatures pretty substantially.

All 7 cards I have taken apart have had dry TIM, almost crusty even, straight from the factory. Changing the TIM refreshed it, lowered thermals, and provided with the comfort of knowing it wasn't going to suddenly heat up and get over heated. All of the before and after are in that thread. I also move from air cooling to water cooling on the 780ti Classifieds, which is a nice change but not necessary because of the ACX doing a nice job.

Now, complaints of the fans and ACX coolers. Google those issues. I know they aren't previlant on all cards, but when the cooler rattles, it make sure you know it. So, changing the TIM and placing some sort of bracing material on the ACX can reduce the chance of rattling.

Here: http://forums.evga.com/m/tm.aspx?m=2146287 is the reTIM of most of my cards, not to include the new 760 or latest Classified. That will save searching.

I do fold, but not constantly anymore, because it is summer. I do benchmark a lot. Benchmarking requires a good TIM job, and stock EVGA isn't quite the same as making it better by replacing it. I don't benchmark all day every day either. I would say maybe 2 or 3 days a month, I focus on benchmarks and getting them as high as possible. The stock TIM, with winter temps coming through an open window, wasn't terrible, but changing it helped a lot. Also, TIM dries out, even if you aren't gaming more than 2-3 hours per day. Especially if you are in a dry location.

I will always suggest replacing TIM often, because it guarantees your hardware to be at its best, and it takes 30 minutes, once every 6 months... If you don't have an hour to spare a year, you are really doing something wrong.

If you don't want to reTIM, then don't. If your card overheats, save your 30 minutes and ship it back to EVGA and wait 3 days to a few weeks... But don't worry, you saved yourself 30 minutes.