Upgrading RAM is really easy. You don't need some "Apple Specialist" to install it for you. Save yourself a load of money, and buy the RAM somewhere else, like from Amazon. And install it yourself.
They are just trying to get more money from you really, lol. The free installation might seem good, but in reality, it isn't when the RAM costs a fortune.
Anyway, heres a link to a random youtube video showing you how easy upgrading the RAM is.
>LINK<
*edit*
Also concerning the lifetime warranty. Maybe I'm just lucky, but over the years I have had 0 RAM go bad on me. And I have 3 PCs and my mini. (also built a few PCs for other people, and their RAM is also fine). And even if the RAM does die on you in a few years time. With the money you'll of saved from buying the RAM yourself, you can afford to buy another set and still have money left over!.
ps. I find RAM usually either works, or it don't. If it works when you first install it, you'll probably end up getting a new mini before the RAM dies. (I think theres software to test out if the RAM is fighting fit, you could look into getting that to make sure the RAM is ok, after installing it).