A few comments....
1. Melanoidins are colors, not flavors
2. adding melanoidin malt to "mimic" a decoction presupposes that a decoction has some effect on flavor
3. I have done blind tastings of decocted vs. non decocted beers 15-20 times and never could pick out a difference in flavor on a repeated basis. When I did my decoction experiment years ago, that was also the conclusion if of over 40 other blind tasters. Now, I'm not saying that I and all those other people couldn't be wrong, but I have to admit that seems far fetched.
4. Like anything in homebrewing, the best reason to do a decoction is becasue you enjoy the process, not becasue it will necessarily improve your beer. We do this as a hobby and as such, if it's fun, do it!