the previous skis you tried may just not have fit you and your style as a skier. there are lots of different skis, styles, constructions, and performances with different skis being designed to do certain things and fit certain styles better than others. the volkl 5star probably best fits your needs.
since shaped skis have come out, i have consistantly bought the wrong ski, sadly. i am always buying a ski for what i am skiing recently and not the ski i needed one or two years later, lol. but after two skis that seemed perfect, i've lined up my current two ski quivver that really balances out my needs. i could use a really big powder board eventually, probably find an nobis inspired on ebay eventually that would fit the bill.
to answer your questions: almost all alpine skis today are "shaped" with exception of a small population buying specialized mogul skis that you generally won't find in the shops. they are really inherently superior in almost every way to the older skis for most people's uses (with exception of mogul skiers or other specialized pursuits). regarding longevity, i think you're more likely to demo and "need" another ski long before your current ski looses it's performance unless you're doing 30-40 days a year. but if you fall into that catagory, you are obsessed enough to fall into the former catagory of buying new gear you demo often.
the five star is a pretty heavy ski iirc, so powder float could be an issue. i can't remember it's exact dimensions... the 724 would be a better powder performer, but as an all mountain ski with occasional east coast powder, you could do a lot worse than the five star. but you could do a lot lot better as well. that performance issue is up for you to decide
