Other than a nice genre filter and some nice list export options I can not really think of anything I especially miss. Granted I do not tend to reflash an entire flash card all at once or add more than a single game at a time meaning my use of such a tool is more about information gathering than ROM management. Equally I recall playing with sqlite as part of it at some point which was a learning experience and one I would probably want to return to now I understand databases a bit better (proper searches possible and all that).
Re: making your own. Ignoring that VisualBasic (assuming you do not mean VB.net in which case ignore me here) is dead it is actually a fair undertaking to make a ROM manager and have it be comparable to the others available, it is obviously not on the same level as writing an emulator or something but there is a lot to consider (trimming, icon extraction, hash checking, header reading, regular extraction, info database parsing* and more) all of which has had extensive discussion on the appropriate methods for some time now or otherwise requires a fair bit of understanding.
*you can make your own but offline list and crlmame pro are the two big formats.