I have heard a couple of disparate points on the subject - is there an indexation/relevance issue found with usign the aspx extension as opposed to the .html extension?

If I switch over to .html down the road, will all links pointing to my .aspx page still functiona and 301 redirect to the html extension?

Thanks!

Some people prefer .html and believe it ranks higher than .aspx or .asp or .php.

Yes if you make the change in the future the old auto-generated product URLs will 301 to the new extension.