I went through the same decision process when looking to add a tour pack to my Street Glide. Initially turned off by the cost of an OEM one from HD. But the more I scrutinized the aftermarket ones, the more I realized the quality just wasn't there.
When adding something to your bike that's as highly visible as a tour pack or lowers, I just don't think you can go wrong sticking with Harley parts. The colors will match perfectly and the item will absolutely be an integral part of the bike's look, not appearing to be an add on.
Now, if you're customizing the look of your bike anyway and don't care if you stray away from the "showroom Harley" look, then by all means explore your other options.
The other reason I went with the HD tour pack was that I feel in the long run, OEM parts will add to the resale/trade value of your bike more than aftermarket parts will.