Well after thinking about it for a few days I think I have worked out my plan to not invest an additional funds in my wife's RRSP other than my current $100/month.
It comes down to taxes.
Situation #1 - In the RRSP (Spousal)
Let's say I put in $1000/year additional to my wife's RRSP. That would generate a $350 refund on my taxes which I would roll over to the RRSP. So I keep doing that I would average $112/month at 5% for 15 years I would get about $32,050. I would get tax free growth until I hit 45 but then we would start paying tax on all the gains and the original investment to the tune of about 26%, or about $8333 of that. So her nest egg after tax would be $23,717.
Situation #2 - Outside the RRSP in my spouses investment account.
In this case the wife invests $1000 in a Canadian Blue Chip stock. Dividends would be taxed at a -5% rate, so better than tax free growth and then once she sells she would only pay capital gains at a rate of about 13%. So we kept putting in $1000/year or $83/month and she got dividends to a tune of 1% for a 6% rate of return she would have $26,592 in 15 years. Now tax in this case is only on the capital gain, so drop off $15,000 for monthly investment to $11,592. Then drop the reinvest dividends for another $115 to $11,477 at a 13% tax rate, she would owe $1492. So the nest egg after tax would be $25,099.
So outside the RRSP beats inside by $1382 and I did not include any bonus for getting that -5% tax on the dividends outside the RRSP.
I should point out those numbers were made with a lot of assumptions (like all numbers are in current dollars, that the wife doesn't sell the stock early and trigger a capital gain, and that any RRSP withdrawals would be fully taxed), but with numbers like these you have to make some assumptions otherwise you can't come up with anything. I still feel that having an RRSP is a great idea for those investments which are tax equal to income like interest or holding non- Canadian stocks.