It's worth as much as someone is willing to pay for it.
I tried to sell my merv with traxxas cvds, hot racing shocks, hot racing steering post, GPM knuckles, proline dirt hawgs, a spare set of rims, the factory body, a proline vw bug body, new unpainted body, 2 3s SPC Racing lipos, RPM a arms front and rear, Rpm knuckles, hot racing body posts, rpm front and rear bumpers, two different sets of rockers, all new bearings, traxxas wheelie bar, 28, 23 and 18t pinions, new chassis, new bulks, new diffs, new wing, new wing mount, a thunder ac6 charger, Traxxas TQI Radio with 5 Channel telemetry ready receiver and a random bag of parts. Before it got stolen by my ex I had it listed for $250 and didn't get a single message from anyone. Most on here will tell you that it's orthodox half of retail and any household and mods done do not add any value.
I have sold plenty of things in my life, including dozens of RC's. What someone is willing to pay will fluctuate greatly depending on what it is, condition, and modifications, so telling me that its only worth what someone is willing to pay goes without saying...what someone is willing to pay is what determines the market.
As for mods, some can boost value, but as a general rule, I know the return on investment of mods is nil...point being however, if someone had the choice between two of the same item in identical condition, but with one having been upgraded to absolve some common problems, the value of that one will be higher than the other to prospective buyers.
So you had one up for 250 and no nibbles. Thats useful info, and exactly what Im looking for. Wonder if anyone else will chime in with what theirs have gone for.