I've had a remap for 5 years, it's driven daily and the occasional track day, and so far so good. It's a little mx5 and I got a switchable Ecutek map with race rom features.
Economy has indeed improved:
Stock mpg: high 20s day to day and low 30s on a long run.
Remap: low 30s day to day and mid to high 30s on a run.
I got 15mpg from 4 laps of the Nurburgring
The power increase was modest, 158bhp to 185ish, but the drivability improvement over the stock map is huge. The tuning guy did lots of small adjustments between Dyno runs to get it how he wanted it.
From memory he did the following:
Loaded in his best saved map for my engine as a starting point.
Then in between Dyno runs he did:
Fuelling
Cams
Knock
Then he did another run and then did:
Knock
Cams
Fuelling
The above order might be wrong.
In addition to the above, he did the following:
Removed the factory 90% throttle restriction for first and second gear.
Ironed out a flat spot at 4000rpm.
Decreased the fuelling at idle by 25%.
At £570 it wasn't cheap, but IMO well worth it.