There's a standard rule of thumb that the higher the quality of gyokuro the lower the temperature needed to steep it, but it really isn't as cut and dry or as simple as that. Nevertheless, some of the best gyokuro I've tried was brewed with water that seemed barely above blood temperature (pre-warmed cups are important) but I don't buy this sort of tea for home - frankly, my brewing techniques aren't good enough, I've wasted enough good tea in the past through incompetence so prefer to leave it to dedicated tea enthusiasts and enjoy their expertise whenever I can.

I would definitely play around with the gyokuro you have, try infusing it at 5C lower than you're used to next time, and perhaps go lower still the time after.

With sencha - which I take many more liberties with and experiment with far more - brewing at a lower temperature than the recommended can have dramatic results (so can changing the water you use - Volvic rather than Evian if you want to try it with mineral water).

I took to sun teas and cold brewing quite late on but that's another way to get different (sometimes surprising) results from teas you already have or are familiar with. It can also give a new lease of life to some forgotten leaves that are past their best, dried tea leaves that might taste stale and "off" when brewed with the correct hot water temperature might recover some of their pre-over-oxidised glory when left to brew overnight in cold water.

I am with you about flavoured teas (why bother when the tastes inherent within good teas can range from the flesh that clings to peach stones to cinnamon to muscatel to nutty biscuits) but there are a few I enjoy on occasion, one of the best I've tried is a tea flavoured with osmanthus. I mention this because a good jasmine tea can be beautiful, and very refreshing, when cold brewed - even in sparking water (drop a couple of teaspoons into a bottle of Perrier and invert the bottle once or twice over a 12 or 24 hour periods, then pour through a sieve)