I just upgraded from a Fuji S2 (which I bought in preference to the
D100) to a D200, and am also an avid amateur, so perhaps my reasoning
and experience so far will be of some use to you.

The D200 has a bigger buffer (about 19 pictures; it depends a *little*
on format apparently) so you can take longer bursts before the card
limits the shooting speed, and it also writes to the card much faster
(I timed it at 7.6 MB/sec to a Lexar 133x card with WA; about 4.6 to
an 80x with WA).   I don't know the numbers for the D100 off-hand, but
I don't think it was far different from my S2, and this is *much*
faster than my S2.  

These cameras seem to have the exposure biased to avoid burning out
even trivial amounts of highlights; yes, they tend to underexpose.
Can't compare to the D100 directly -- but there appears to be a custom
function setting that does permanent exposure bias in various modes.
If I'm understand that right (haven't used it yet) you can use that to
fine-tune the exposure to match your preferences.