For only mild off-pavement, I'd replace the 100. It makes for a great daily driver. Been driving up and over 10,000ft passes without any issue passing at 65mph. Sound system rocks, seats are far more comfortable, wheel is heated(I know I know you're in Vegas) and I get noticeably better fuel mileage than even the stock 2005 LX.
Perhaps with a slightly tougher tire and one inch taller over the 30.5s I wouldn't hesitate to drive it on almost all of the trails in the San Juans and I'd even take it on the easier Moab trails.
I like it and really I don't feel like driving the 100 anymore, but that's the real utility vehicle. In the LX even with a fridge replacing my 40 split seat, a subwoofer and a full drawer system I seem to have more space than the GX.
For most I'd say for a daily vehicle the new GX can hold its place if you are looking for something trim compared to the overblown LX570/LC200. If you have a bigger family or want to wheel/go camping a lot, etc....go with a late 100, and dump the savings into mods.
For me, currently a 100 is tough to beat so I plan to keep at least one of the 100s and the 150 for quite a long time to come.