the things the DAV gear offer is based on design & theory that is not going to change significantly in the foreseeable future. It is not 'fashion' of the day stuff. If you are deriving revenue from audio work the BG1 will eventually 'pay for itself' (the less revenue, the lower the profit, the longer that will take) Buy one and you would expect to last your life time (more or less) . . . it's a mature design with 'better' being largely subjective (is this cap better then that cap, etc.)
Roughly speaking the BG1 falls into the 'straight wire + gain' group of pre's. Doesn't mean that it doesn't have an individual effect on signal but you don't typically buy one for it's boutique, fashionable sound. You get it to stay out of the way of original signal as much as possible
There is probably not a lot to be gained, particularly from mics you list, between BG1 and Duet (I am probably prejudiced towards believing that the BG1 is probably a better mic pre (while 'different' I think four channels of DAV compare favorably with four channels of API (3124) for lower investment) (and the single number of amount of make up gain can never be the complete picture) but my experience with apogee is also universally positive and gut feeling is that you are not going to notice a huge difference
If you have to spend money just to spend money anything you do to 'control' the room in which you record (or even more importantly edit/mix) will probably have better cost/benefit return
after 'room' I also subjectively reacted that different mics might present a more dramatic improvement in sound . . . but that tilts too close to appearing to be critical of your mic list, which is not really the case . . . merely that my 'taste' runs to different mics
