It really depends on your customer and the area that you are working in.
Some government bodies require twin engines for "safety" and possibly speed so that rules out your 210 to an extent.
Based on what I have seen from a local Aero Club that does fire spotting, they ditched using 210's and were last using a PN68 and 404 Titan mainly because of the speed. Once a fire is spotted they want to get there ASAP and check it out and decide on ground crews and aerial action.
If you're after something for "spotting" as such, then speed is your friend - but depends on your target area.
If you want something for observing and coordinating from an aerial perspective, then a 172 would do the job.
The club that I observed doing the spotting was using PPL's with the CFA observer which was a good way to clock up hours.