Depends on what VH timeframe you're looking for. Early stuff, I'd say get a Holy Grail reverb and set it for a hall reverb setting to get a big sound. For later stuff (and with your 5150, it would work great) I'd get a Boss DD- 2 or later delay and set it for about 500 ms. Both of these would be in the effects loop
. If your looking to buy something though, try and find a Alesis quadraverb GT and put it in the effects loop on the post EQ setting. Don't use any of the preamp controls. Set all preamp stuff to zero and just use the effects. the preamp in it smooths out the sound and sounds just like the Right Here Right Now CD. Should be cheap and you can nail that 90's VH sound perfectly.