I have both the DSA815TG and a Tektronix 2754 spectrum analyzer (which is a slightly "better" version of the 492). The Tek spectrum analyzers are hopelessly complicated, not particularly well thought out in the user interface area, and are not for the novice when they need repair (assuming you can get the microwave assemblies).
If I'm looking at spectra below 1.5 GHz, there is no reason I would ever turn on my Tek 2754. So if you are sure that you don't need/want higher frequency coverage, get the Rigol. A simple choice in my opinion.