The moving map on something like a KLN89, or even a GNS430, I find rather useless
That I agree with. The KLN89/94 and GNS430 units I regard as nothing more than text-based route entry/management boxes. That job - styled I gather on the old FMSs - they do very well. My KLN94 does exactly what it says on the tin, and with total clarity and reliability. If it wasn't for that total crap called PRNAV
I would keep it for ever because it does everything required in the real world.
If flying VFR, you'd often use waypoints that are not in the GPS database, wouldn't you?
No, never. Use VORs, NDBs, airway intersections. The only time I ever had to enter lat/long was for LEAX which in 2003 wasn't in the Jepp database. When one goes abroad, the last thing one wants to do, when asking for some CAS transit, is reading off some village name as the waypoint. Brit ATC don't like it much and foreign ATC even less.