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I have a Mesa Single Recto half stack that I bought 2 years ago. I have never changed the tubes as I didn't realize it was even an issue until reading up on it here over the last few weeks. Is there gonna be that much of a difference? Will switching them be worth it? Lastly, doesn't Mesa put pretty decent tubes in their amps at the factory? All in all should i replace them or what kind should i replace them with?

Mind you I'm not unhappy with my sound but there's always room for improvement and I keep seeing everyone says what an improvement there is.

you will probably notice a significant improvement if it's been 2 years since they've last been changed. tubes wear out slowly over time and it's hard to notice until one day, you'll hear that your tone is just lacking.

with fresh power tubes you will probably notice that your amp is a little louder than before, and with fresh preamp tubes you will probably hear that you amp's tone has just improved overall. and if there's any noise (loud buzzing, squealing, ect) that should be gone with the old tubes.

i've always just stuck with the stock mesa power tubes and i don't have any complaints about them. i've heard of others getting good results using JJ power tubes, but you have to make sure you get ones with the correct rating because you can't adjust the bias on your amp. talk to bob at eurotubes.com and he can hook you up.

as far as preamp tubes, i've tried sovtek, JJ, and electro harmonix, in addition to the stock mesa tubes. i tend to lean toward the JJ's or the EH.

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I don't wanna knock Bob at Eurotubes, but what tubes do you suspect a JJ salesman is going to sell you......you guess it, JJ's and that's it. he he he

If you've been using your head at loud volumes quite a bit in the past couple years, you probably should get new power tubes. If you've used it at low volumes pretty sparingly in the last 2 years, they may still be fine.
If you change them, I'd get Svetlana =C= logo 6L6's.

Preamp tubes are where you'll notice your amp's preamp tightening up and sounding better. For highgain amps, I always recommend Groove Tubes 12AX7C's, which are $14 each.
Everyone who's taken that advise has been happy and thanked me after they did it.