I agree with Warped04 to some extent in that you should try to figure out why a batch didn't turn out quite as you expected, and then experiment with multiple successive batches to try to fix whatever the problem was. However, there is no reason not to play with post-fermentation fixes in order to improve what you have already. Blending is one of several options. Sometimes, two marginal beers, when blended, turn out to be excellent.
Before brewing a "blending beer", I suggest trying blends with beer you already have available. Before doing even that, you can try to fix the beer without blending:
If it is just a lack of mouthfeel, you can add maltodextrin to the beer to make it taste a bit fuller. Adjusting the carbonation level will also change the perception of mouthfeel. If the malt character isn't coming through, adding some calcium chloride will round it out a bit. Just pour yourself a couple of pints and play with it. When you find a method that results in a better beer, scale it up and blend it with the rest of the batch. Good luck!
Most importantly - wait a bit first before playing with it. Letting a beer lager for a few weeks can change its character a good amount. Maybe time is all you need to fix the issue.