I've a GNS430 and GTX330.

1. My aero radio people tell me that they think the GTX 330 display
is always up on the map. I.e., I can't declutter or eliminate it if I
want to, say while flying an instrument approach and not really
needing/wanting the mode-s traffic info on the screen. True?

You can disable the traffic display any time you want.

2. I assume that the traffic warning in the mode-s will not alert to
traffic if I'm not in a mode-s area, and/or there are aircraft only
only squaking mode-c or other. In other words, if I'm fling along out
in the hinterlands (a frequent occurance) where there is no mode-s,
the traffic warning is nonexistent!! Wouldn't I do just as well with
a portable Monroy, or similar, traffic alerter?

You need to be in an area with TIS coverage. In California, for
example, the Bay Area and the area from Santa Barbara on south and
east towards Palm Springs has TIS, and it works great.

-jav