There are plenty of SOLID Ti 1st stages out there. Not recommended for use with 40%+ EAN though and some manufactures recommend there use with either EAN or air but not both, Dont quite see the logic there. Also many 2nd stages also have SOLID Ti parts.
The bennifits are resistance to corrosion and weight. Not to mention wank factor.
As for Ti valves, well I dont think corrosion is such an issue, weight deffinatly isnt but there is stall the wank factor. So maybe if you have some spare cash and know a good machinist they could whittle you one up.