Just ran PVC conduit inside my mast. Wasn't easy (mainly do to lack of experience), but DEFINITELY worth it! So much quieter. Used rivets on the leading edge of the mast.
Lessons learned:
The yard manager predicted that a lot of the slapping noise might have come from internal halyards. Not true.
Used #200 conduit to withstand the rivet. Had to go to a landscape supply. Home Depot etc., only carry lighter pvc. The lighter PVC would probably be okay if you are using adhesive, but I think it might pull trough rivets.
Wasn't sure I could remove the upper halyard sheaves, which made it difficult to feed the new wires through the mast, so I chased the old wires with different colored mason line when I removed them. This was a BAD move. The mason line eventually snagged any screw or rivet it encountered inside the mast. If I hadn't been able to remove the sheaves (turned out that I could), I should have used the electricians pull line available at any hardware. It has a waxy finish and is not prone to snagging as the mason line was. Thought I was being clever using colors to I.D. the different wires. Turned out to not be so clever or necessary!
With the sheaves removed, I was able to use a fish tape to run the lines.
On the horses, I had to flip the mast (leading edge up) a couple of times for access to certain holes, and to get rid of the birds nest I created with the mason line. I forgot that I left it in that position the previous day and wasted some time routing the PVC on the wrong side of the mast before realizing it.
I should have marked the leading edge with some blue tape at the mast base. It sounds silly, but it's not hard to get confused.
The spreader light wire holes in the side of the mast are small and were a nightmare to feed the new wires through. Because they were on the sides of the mast (not in front), I was reluctant to enlarge them without someone's (a rigger, engineer, etc.) OK. In retrospect, I should have obtained that OK. Instead, I struggled.
As tempted as I was to use the adhesive method, I couldn't figure a way to do it without being able to remove the mast head. Knowing what I know now, I still can't imagine being able to do it.
In any case, to answer the question in the OP: Even as difficult as I made the project for myself, every time I step on the boat I know it was worth it!