Please clarify whether differential output ports PDIVOUT & NDIVOUT needs balun transformer or not.
Is there any degradation in spurious performance if balun transformer not used at the differential ends.
This is a bit of an open ended question as you provided no details about your application, frequency range or mentioned which spurs (PFD, fractional, integer boundary, reference) are a concern.
The differential outputs can be used singe ended without a balun however DC blocking should be retained; I would expect the spurs to be generally be worse without a balun as you lose the benefit of the common mode rejection. If the frequency range is narrow (10-20% BW) there may be a slight increase in output power; broadband baluns will have higher insertion loss negating any improvement in power but should typically still offer some spurious improvement.
We saw some improvement in particular with respect to the 1/2 harmonic (probably 2nd as well) but admittedly our testing was very limited.
I recommend that you verify the performance for your frequency range and application (over temp) if spurs are a concern. Also I recommend you stick to using the LT3042 / 3045 regulators and pay attention to their layout (refer to their datasheets for more info) as well as the synth layout if spurious performance is important.