Share with us the improvements you'd like to see. You did list the neck and weight, to be fair, but those are largely subjective.
I'll never own a Sire (too many basses as it is), but I'm always curious about poor reviews with few specifics.
Those two things were my main gripe. As far as being subjective, I never weighed either bass, but both had to be in the neighborhood of 11 lbs. That,..is pretty damn heavy. As for the necks, the 5 especially, felt much more like a P bass than a jazz to me. Thick front to back, round baseball bat feel , rather than flat and wide, my personal preference. Very much different from a typical jazz neck feel. The preamp, while very versatile , had almost too wide a range. Bass control being the biggest culprit. There was so much bass boost available , you seriously could do speaker damage if you weren't careful. I wound up preferring the tone of both Sires passive, and I'm normally an active bass kind of guy.
The neck on the 4 was closer in feel to what I prefer, but once again, the weight was substantial. To me, there's no reason for a 4 string jazz to be pushing 11 lbs.
I truly wanted to love the Sires, my family actually bought the 5 for me as a birthday present. Unfortunately, it just wasn't a fit. They make a decent bass for what they were charging back then, but seeing them in the $1500 range seems like putting a set of expensive chrome wheels on your Ford Fiesta. Once again, no offense to the folks who play and love Sires. We all have different tastes. And while I'd rate the Sires a bit higher than I would a Squier, can you imagine the comments if Squier released a $1000 - $1200 instrument? Both companies were supposed to be a decent budget brand. I'm sure Sire will sell a few of these , I could find some other extremely nice basses for sale at that price point though. Case in point, a Dragonfly just sold for that price here in the classifieds. Hope that answers your question.