I had forgotten how complex your property empire was!
Right, you're both in your early 30's?
Wife to be currently earning c. 20k, but once married she'll be pushed into higher tax bracket with her share of rental profits (assuming you've that aspect of planning in hand).
Once she's paying tax at higher rate, she'll get higher rate relief on any pension contributions (technically she'll get 20%, but she'll have more of her 20% band left to use for rental income, so she will get relief at the higher rate).
However, the amount she can get relief on is based on a percentage of her earned income only. So in her 30's it's 20% of her 20k, or c.4k per annum. Even at that rate, with no growth, it'll add up to over 120k by retirement age. Tax free growth, tax free lump sum, etc. I wouldn't dismiss it at all. Especially if there is an matching contribution from employer.
I'm sure I'm missing loads here.