that depends entirely on your area. around here a first gen with 5K miles and mods will sell for mid~high 3's. In other areas, a first gen sells for high 2K low 3K, (FYI, this is asking price, I don't know what these bikes actually sell for.
Also, it really comes down to what you are willing to pay for it. something is only worth as much as somebody is willing to pay for it. are you willing to pay $4500 for a gen two SV650 that has low miles and is in mint condition, or are you willing to wait for the same bike to come along that is priced at $4000.