I have an '89 MIJ P-Bass which I love to play but sounds weak compared to my vintage G&L's. (L-1000, L-2000E and SB-2) So, I'm considering changing the pickup and the Darkstar option is intriguing. The expense gives me pause because it looks like I'd have to replace the tort pickguard I just put on it in addition to the routing. If anyone has any advice based on their experience, I'd appreciate it. I would also consider other types of pickup replacements. I mostly play Classic Rock and Blues.
Personally I would find a cheap body and pickguard to rout and leave the MIJ alone unless you absolutely know the Dark Star tone is for you. A DS tone isn't exactly "classic rock and blues", just sayin', imho. I have several DS's basses and sometimes I still need a P-bass. Since you mention the bass sounds weak, Fred Hammon has always said the DS is not a magic cure...it's best suited for improving a bass that you already like the tone of. In a hollowbody they are magic, but that can be a wash in a solid body. Just sayin' since you're looking at a commitment of a few hundred bucks.
The P isn't an SB-2, it isn't an L series. It's a P. The relative volume levels between those are irrelevant. Celebrate the tonal variation that the P give's ya by adjusting your gain staging ... I've had a DSP. It's with BartmanPDX now. I liked it a lot. A different flavor of bass for sure. You have classic rock and blues dialed with your current basses though. A DSP isn't really going to add much to that - IMO. ... and personally I wouldn't be playing Mr Happy Router on an 89 MIJ P ... I have a MIJ 87 (62 RI) and it's a fine instrument. I did a pickup replacement as I wanted something more 'vintage' sounding. I went with a custom build from www.vintagevibeguitars.com that has worked out pretty well I think. I did a sample for them that I think is up on their site now. I'm just embarking on a new DS project. This time it's going into a Samick Royale hollow body. In the 'ray humbucker position. I expect it to be a really different flavor of bass when it's done. It's different for everyone as our musical settings aren't all the same. At the end of the day for me, when I add a bass into the quiver it has to deliver some variation from what I already have. On stage I generally run 2 basses. 1 with flats, 1 with rounds. Close cousins tonally so I can use one as backup in a pinch, or use the flat's vs rounds through the night. I run a Radial Bassbone to adjust for volume differences between the instruments I pick for the evening.