1. Will MoI and Silo compliment each other

Yes

2. Is it overkill to have both MoI and Silo

No because if the answer 1.

3. If only one is needed to model what ever might be asked of me to model, which would you choose (non biased please)

I would say Silo > MoI ... You can actually model everything you want with subd's (silo) ... it's less accurate for hard surfacing, and way more boring
in some area (forget booleans way of modeling :P), but with some patience and skills it's possible.

The opposite it's not true, now way to do pure organic modeling in moi with the actual tool set. And even if the toolset will be enhanced in the
future, it will never be as flexible as poly/subd's can be, whatever the task.

4. Would you say forget MoI and Silo and go for....

Good question ... this required to well know the other packages around, and I didn't ... I like modo quite a lot for rendering/poly modeling
(mostly because I'm coming from lightwave so there are no leaning curve) ... But again, if I can, I jump in MoI every time it's possible.

Btw you should read the CG Channel review, it's a good way to know the benefit and the limits of MoI.