Proof Like

No, it cannot be PL over time, it would be struck that way. Yes, PL does add to the value, especially if it has very deep mirrors (DMPL).

This is just a guestimate but maybe 20-30% premium? Here's an another source for prices that I use a lot:

http://www.numismedia.com/fmv/fmv.shtml

It has listings for DMPL Morgans as well as regular. Keep in mind these are retail prices, not what a dealer would pay you.

They can only be DMPL if they are uncirculated - so I think the bigger challenge would be trying to figure out if they are MS60, MS61, MS62, etc. One difference in grade can make a big difference in price. I have spent some time learning to grade coins but when you get up into the uncirculated grades, it is a much harder thing. You really have to know the series EXTREMELY well. (I admittedly don't)

Also, DMPL is kind of subjective I think. The coin shows on cable/dish tend to put them under a bright light and rotate them and say "oooo - look - mirror finish" - but anything will look like that if you put a 1000 watt halogen light on it.

Common date uncirculated Morgans go for $30-50 in typical grades. More for DMPL - $50-70 maybe. I'd try to see if you have any key date coins as well as it might be worth having an expert appraisal.

Best regards,
Ken

PL and DMPL coins are tough to image, but you'll know 'em when you have 'em. A true DMPL coin, one which will grade that way by a TPG, will show such reflectivity that you can read 12pt type in it at a minimum of 10". A PL coin will be readable at a lesser distance.

There are a lot of very shiny Morgans around. If you can't read 12pt type reflected from it, it isn't Prooflike.