Well, if you don't need to do any aqua assualts in the near future, I would suggest looking into the P226R. A basic P226 with the rail now standard, everything you need without the marine finish. And it should be less money than the Navy version. There's nothing wrong with the Certified Pre Owned Sigs, either, but if you really want the rail, I wouldn't go that way.
Also, check out http://www.sigarms.com and check out their warranty info. To the best of my knowledge, Certified Pre Owned Sigs do not have a lifetime warranty. For that matter, I don't think new Sigs do, either. However, if your dealer said there was a lifetime warranty, ask about the distributor they get the gun from. If they are getting it through a distributor (which they probably are not because I think Sig has gone completely factory direct), the warranty may be seperate from that distributor, in which case that is a good thing to know because you'll need to contact the distributor, not Sig, if something is wrong. If you want to ask questions about the warranty on a Sig you are interested in, drop an email to their customer service. I dropped them a line recently and they were very quick to respond.
I've owned a P226 40SW for four years now, so I most definetly think you have made a wise choice. There are, however, a lot of various P226 options. They're all at that website I gave you above. But the P226R will probably be the least expensive as a new Sig and will cover everything you seem to want on and from your gun. Good luck!