[kathyricks]

You might be hard pressed to find anyone on the Sequoia or 1stGenTundra forum who has had their valves adjusted because no Toyota V8 (except the 1990-1994 Lexus V8) ever had a reputation for developing loose clearances over time.

That said, one way to confirm whether or not some of the clearances on your particular engine are too loose and ticking without spending a huge amount of money is to have the dealer remove ONE valve cover and CHECK (not adjust) the clearances on one of the two cylinder heads; i.e. check the clearances on 16 of your your engines 32 valves.
It shouldn't take more than about 2 hours worth of labor for a dealer to do that + $30 for a new valve cover gasket).

If indeed the dealer finds some of the clearances are too loose, then a good time to have them adjusted would be when you are due for a timing belt change because the timing belt needs to be removed in order to adjust the clearances (the camshafts have to be removed which requires the timing belt to be removed).

Driving a long time with loose valve clearances won't damage your engine (won't wear down the tip of the valve stem or the valve lifter it contacts) so you shouldn't worry about excessive wear, but engine power and fuel economy will not be optimal if some clearances are too loose.