I was told by the guy in my LFS that tanks should be replaced after 10 years as the silicone tends to lose it's strength and cause leakages. Is this correct? I've also heard you can get them re-sealed, any issues with that?

Just looking to the future!

Hmm... ive never heard that. My parents had a 30 Gallon when I was like 2, and they used it for along time, and put it up, and then used it again... and never seemed to have problems with it. Sounds like it could be true. I know you can buy aqarium sealant, so I assume if the silicone did because weak, you could re seal it. Doesnt seem to hard to do.