Well, I am obviously a bit biased but I'll try to answer these as honestly as I can:
Signal generator - calibrated frequency and amplitude accuracy (i.e. repeatability)
You (as the user) can calibrate the frequency as well as the amplitude. Frequency calibration might not be necessary, the TCXO has a tolerance of 1ppm. Amplitude calibration is definitely necessary if you require accurate output levels (without calibration they can be off several dB). You can calibrate the amplitude at up to 64 frequencies, it will be interpolated between the calibration points). Repeatability on my device after several months is better than 0.7dB (amplitude is still spot on compared to my SSA3021x which has an amplitude accuracy spec of 0.7dB)
Signal generator - harmonic and other spurious suppression.
Not good. There is a bit of filtering but you can expect a lot of harmonics. It is okay if you just need "any" signal at a specified frequency but it certainly is not a clean signal source.
Spectrum analyzer - calibrated frequency and amplitude resolution, accuracy
Same as with the signal generator. Both amplitude and frequency calibration is available, amplitude calibration is necessary to get good results.
Spectrum analyzer - resolution bandwidth, max span/points, sweep rate
RBW from 13 Hz to 112 kHz, maximum span is 6 GHz (but unreasonable slow at that point), number of points is fixed at 1001 (but this could be changed in the source code). Sweep rate is generally too slow for wide spans (e.g. 8.5 seconds/100 MHz at highest RBW). At low RBWs a DFT acquisition mode speeds up the sweep significantly:
10 kHz span with 100 Hz RBW: with DFT 1.7 seconds, without DFT 130 seconds.
The SA also includes a tracking generator option with a configurable frequency offset (useful to measure mixers).
VNA - dynamic range, calibrated repeatability, etc.
Fairly good between 10 MHz to 3 GHz. Minimum specified dynamic range is 90 dB for these frequencies but with narrow IF BW and averaging, most users actually report something between 110-120 dB on S21. Dynamic range decreases sharply at around 3 GHz, you can expect 50 dB dynamic range up to 6 GHz (better at most frequencies but there are some bad spots in there, so this is what I specified).
You have to keep in mind that the LibreVNA was primarily designed as a VNA. The signal generator/spectrum analyzer modes are sort of an afterthought. The hardware is already there so I thought it would be nice to include these functions in the software but it isn't optimized for them so you can't expect the best performance.