Haha, I don't download much from any filehosts. However (and this is a big "however") when I do want to download from a host I have a 100 Mbps Download speed--I want that file and I want it NOW.
That said, my biggest reason for wanting the Lifetime Premium isn't the download; it's the upload. I don't like uploading rars or split files; I like single-link, zero-extraction (this is why I use MegaUpload as my main host at the moment--I have 28TBs uploaded to one account and everything is named coherently/organized, and everything is in single links).
So, I want to be able to upload all those large large files; but if I'm going to upload so much to a host, I also want to be able to access those files quickly whenever I do need them, and I want to know that I'm going to be able to access those files 2 years from now with the same ease (since, like I said, I don't actually find myself wanting any of it for myself now, but I enjoy the knowledge that when I want them they'll be there).
So, I'm not interested in paying year-to-year (or even every two years); I want to be able to spend the money, start uploading/organizing (and hopefully sharing), and not have to worry about where I'm going to be down the road.
All this said, if you really don't pressure users much to buy premium accounts, then the idea of a Lifetime option should be all the more sweet--I'm wanting to give you ~$150-200 for a service you don't think I need to pay for so that I can upload larger files (incentivizing others to buy premium accounts) that (definitely) won't earn me as much money as they would if I rarred them (I've never seen a host have different rewards for files that were 5-8GBs, and definitely never seen ones that had a different payout for 50GB files).