Here's my D30:
5.13s, aussie locker, Nitro axle shafts, C gussets, control arm skids, custom truss/brackets, Poly ball joints.
Locked on 35s for 3 years of hard wheeling. And I am going to be running 37s on beadlocks here shortly now that i trussed the 30 and added hydro steering. If you want to build your 30 go for it. Alot of people bad mouth it but the fact is that once your gears have worn in - assuming they have been set up correctly and broken in properly - most of them are pretty solid. When the JK 30 came out, it had a significantly thicker ring gear. I'm not saying that makes the ring and pinion anywhere close to bomb proof but it does add strength over the previous generation D30s.
I don't know if its worth the money to go 30 spline, but i will tell you that the Nitro shafts are well worth the coin. They use the same size U joints as stock rubi shafts - must cromo shafts use the smaller 4130 size. The ears are just enough to be thicker than the regular 30 ears...and they are all cromoly. I have wheeled them with the spicer u joints they came with and it is holding up fantasticly. I ordered mine from Jeep Add Ons on here - i think i dealt with Chris. I got one of the first sets produced.
I highly recommend the nitro shafts. I don't really wonder if or when my 30 will break.