I think that two separate lines would be better than trying to convert back and forth - or maybe just give store credit or something to folks doing conversions, rather than putting a staffer on it.
That said - 4e needs the support, going by the two (2) adventures* from WotC that I looked over as possible conversion material. So, keep on making adventures for it. (For what it is worth, I was not overly impressed with their 3.X adventures either, they needed the help back then too. WotC had good rules, but the adventures... not so much. They needed more meat, some gravy, a touch of garlic, or something. The 4e adventures felt much the same - more a series of encounters than a cohesive whole.)
Pathfinder has better adventures than 4e, Paizo does an excellent job of involved adventure paths, but the simple dungeon crawl is less well represented, so there is room there as well.
But I do not think that either stat free or official downloadable conversion is the answer. I wish that the current PDF market was more robust - shortish dungeon crawl adventures appeal to me much more as PDFs than print. Heck, I buy the Paizo adventures as PDFs, and they are not all that short. Lower risk than a print run, but if the PDF market is still depressed, not likely worth it. But I would love to be wrong.
The Auld Grump
*Translation: My experience of WotC 4e adventures is extremely limited, there may be some worth converting, but the two I looked at were cold pancakes without syrup or butter. Nevertheless, I will give you my opinion.
*EDIT* Two food analogies in a single post? Maybe I should have eaten before typing.