Tuning duplexers is a big part of what I need to be able to do so A tracking generator would be necessary.
Many R&S SAs like the FSP KE5FX mentioned have an option called "external generator control" which allows to use an external RF generator (i.e. R&S SME/SMIQ, but also some non-R&S models like the Agilent ESG Series) as tracking generator, which is quite neat. Retrofitting the option on the FSP if it doesn't already have it isn't overly expensive either (I paid less than GBP250 for the parts from R&S, installation takes less than half an hour).
Considering that the presence of a TG often raises the price by 50% or so, ext gen control might be a decent alternative. Plus the RF performance of many TGs isn't as good as a standalone RF generator either.
As to the FSP itself, be aware that there are two variants out there, the older ones (1064.4495.xx) have a beige/grey front bezel and run WindowsNT on a slow Pentium3 controller with PATA hard disk, while the later ones (1164.4391.xx) have a beige/blue front bezel run WindowsXP on a Pentium-M based controller with SATA hard drive. The newer variants also have some other improvements, i.e. in the RF sections. Should you opt for an FSP then I'd strongly recommend looking at the later models.
The FSP UI isn't that bad, many things just require a few more button presses than on many other analyzers, but main functions have their own front panel buttons.