Yes... I'm really not that great a composer or musician generally yet, especially with the SID but it does occur to me that you want to be using the voices for melodic parts rather than chords.
Also, having two voices for SFX would be much nicer but that's quite possible when you have two SIDs to use. I'm betting though that on the M65 most SFX will be done via the DACs.
I think the value in the saw waveforms I propose is that there is more harmonic content in them to play with and they free the filter and voices for other things. We both see the value in a real white noise.
I concur that the sine waveform has little value other than being a filler or useful in assisting in the generation of the "natural" saw. It would probably be "expensive" to implement, too. But there could be times where it is of use and would pad out the range of available tones.
Honestly, the SID is quite awesome, even today. I just think that, even when used properly, the sound has become a little stale because there is a limit in the number of tones available. A few more to play with would give it a fresh appeal.