Thanks for all the responses thus far. Based upon all of the input, I've
determined the following is my best path forward:

1. Ditch the Colt and go back to the Bosch 1613. Having used the Colt for
test cuts was leading me to that conclusion anyway, it just isn't built for
that kind of extended hard use. My purpose for using it was because I did
have a way to fix the router base offset on it while not having a similar
capability for the 1613. The small router also has a tendency to chatter
and depth adjustment has been less than simple. However, I'm seeing the
same kinds of gaps with the Colt as I was seeing with the 1613 when I used
it on previous projects, so this just returns me to my starting point.

2. Because of the centering issue and because I would prefer to use a PC
style screw-in bushing: order one of Pat Warner's clear router bases for
the 1613 and probably the centering kit to aid in getting the alignment
correct. This will alleviate the centering problem and might address some
of the gapping by making sure that the base is uniformly flat -- I was
seeing gaps before, even when presenting the same side of the router to the
template (I didn't try the 180 degree rotation until this time) so flatness
may have been an issue with the 1613.

3. Reset all of the finger guides, starting from the left and using a
machinist's square to ensure the finger guides are square to the guide bar.

4. Verify that the guide bar is uniformly distanced from the work piece
along the entire work piece width.

5. Pay particular attention to technique to ensure that I'm not rocking the
router or tipping the router.

6. Take a very serious look at the Akeda jig. After looking at it on-line,
I see some really significant benefits to this vs. the Leigh, particularly
from the router support standpoint. The only downside I see is having to
change out fingers each time one changes from pins to tails. I'm good with
the 1/8" discrete steps and can live without infinitely variable spacing if
the discrete setup guarantees that the fingers will be positioned reliably.
The only uncertainty then is that the fingers are precisely machined for
repeatability.

--
If you're going to be dumb, you better be tough