That's a tough one. I was facing a similar decision myself, until Dargin said in the Dallas question thread that there will be no piezo offered on the 20th SR5.
A BD Bongo5 H/piezo fretless is likely to be in my future...unless by some miracle a BFR Mahogany Bongo like the Open House bass happens.
The 20th will no doubt be a beautiful instrument and well worth owning. So will the LE.
Flip a coin....
Regarding collectibility, well, both are going to be pretty rare. Only 10 BD Bongos like that? I doubt it. I think the production numbers will be quite a bit higher. Besides, I have a feeling that most of us could not care less about rarity. These basses are meant to be played, not worshipped as a priceless collectible.