Voidmoji
Perpetually Perpetrating Plots & Ploys
Tool kit games are definitely for those with some spare time. Or those, like me, who are happy tinkering away at a campaign setting as a hobby in itself.
I gave up on GURPS 25 years ago or so, and have come back to it recently. This is part of the reason why. I, too, am a constant tinkerer. In recent years, a lot of my tinkering has been working on my own game systems. While I have a lot of work into two different games, to the point of being somewhat playable, there is a home stretch that I simply can't manage to get across.
Rediscovering GURPS has been great, as it allows me to tinker, but in a manner that is much more likely to see actual play. It helps that 4e seems very geared towards options for inveterate tinkerers.