Well you wouldn't be able to sum a variant column either. The CLR type would help in that it could internally figure out the type based on a ruleset, and perhaps return that type as part of the string .... so at least you would know what to convert it to. Obviously if the information is just being passed right out of the database layer then it probably makes no difference.

XML might help in as much as you can create XML indexes on the column. Do you know what type of value is being inserted at the time? If so, you could store it along these lines:

<Info ProductStatus="1" Reseller="0" PromotionStartDate="20080101" />

If you don't know, then it's always going to give a string value and you may as well just use a varchar.