Saving up for the better bike sounds like a good choice. Especially if you love riding out on the trails regularly, spending more $$ up front will save you $$ down the track. The more you get into it the quicker you will outgrow the bike you're referring to, not to mention componetry wearing out & then not being worthwhile replacing.

Best to go to a good entry level hardtail that comes with a good frame & fork from a reputable company (Specialized, Giant, Trek, Norco and loads more). The frame you get is often the same as the higher end models, so as components wear out you can just replace or upgrade them to make your bike even better or lighter etc.

Good entry level duallies will be twice the price - and don't settle for anything less if you want to go that way because it will be money down the drain. But you probably already know that - the don't get the cheap wallmart type duallies!

I think bike fit & being comfortable on it (saddle etc) counts for alot more than wether you have rear suspension or not. I recently got my first dually (went from a hardrock comp) and it's a fantastic ride in comparison. I was ready for a better bike though after having the hardrock for 5yrs, and consider too that sometimes it's better to buy a new bike than upgrading things on a old one.

Once you get your new bike - whatever it is, as long as it fits you well & is comfortable to ride I think you'll be in heaven!