I have both:
The Mustang bass is perfect, for me anyway. I really like the pickup, and this is important: if you're not 100% on the mustang bass pickup, then changing it will be a hassle. There aren't really any commercially available alternatives (short of having a builder custom make one for you), and the body cavity route is a tight fit, so it would have to be enlarged to accommodate something different. But if you like the sound and feel, then it's a great bass "out of the box", since all the parts are top-notch quality.
The Squier Bronco sounds like ass, but as you said that's an easy fix for this one. The body route for the pickup is actually quite large, you could probably fit a precision pickup in there with few hassles. The tuners are quite cheap, I plan on replacing mine. But despite the minimalism of the bridge, this part holds up fine. Mine intonates perfectly and it feels like a solid part. Mine is staying on.
I bought my Mustang bass in December, before the price hike (I paid $600 Canadian). It was a good deal then, and I adore mine, but now that the price has ballooned, I'd say the better value is the Bronco. The cost of customizing it to all your preferred specs will still end up costing you much less than the Mustang bass. For the new price of the Mustang, I find it ridiculous that they don't even include a gig bag. If I hadn't beaten the price increase, I would have only bought the Bronco.
Oh, and another detail: the Squier has shielding... and the Mustang bass doesn't!
Here's a
link to axemusic.com (I think they're in Alberta), they're offering the Bronco bass for $165 Canadian.