Just how much it's really worth, that's something only you can decide. Bikes in this price range are doubtful investments at best for adults. They tend to be heavy and perform poorly. More important, salespeople at such stores don't know bikes. For example, try to get as much chromoly and as little hi-tensile steel as you can.
Alloy rims are another great upgrade.
Any suspension you find at this price range is probably not very good. This is where you can find truly nice bikes without spending an arm and a leg. Unless you're really going to get into cycling, the bikes in this price range have all the features and performance you'll need. A year down the road, you'll be glad you popped for a bike in this price range. From this point on, you're going to get fancier parts, materials, and designs, such as special shifting systems, exotic materials, and shock absorbers.