Since you already have a good assortment of both basic and bike-specific tools a kit will probably have a lot of duplication. I'd consider keeping on the path you are on and just buy them as you need them. Of course don't turn down a bargain you might find at a garage or estate sale. Get a good cable cutter; Park and Shimano make good ones and my Felco, while costly, is of the highest quality, works beautifully and will last forever. Get a good steel rule for measuring chains; I don't trust the chain checkers and it is also generally useful. A third hand tool is handy when you need to install cables and don't have a helper available. A good, purpose-made pedal wrench will save you a lot of grief.