Tuning on the Toyota V6 isn't cheap, partly because it's a very limited market. Some people are happy to pay tens of thousands to get to 500hp with their V6 in a race Exige but for a road car I question if it's really worth thousands to get a few tens of hp.
On the Evora a few mods to headers, cats, exhaust, air intake will get 10s of hp but will you really notice on the road? You'll probably notice the change in the noise rather than the extra power, and that's an OK reason for modifying too.
I've been on road trips with a mix of 280, 345, 410 and 430hp Evoras and there's never any sense of the lower powered cars not being able to keep up, even on derestricted roads like the Isle of Man. Of course you'd notice it on track but on the road it's more about how fast people are prepared to drive and the handling of the cars than outright power.