And I'd recommend putting the original pickups back in, then sell the Miracle Man set separately. You'll get a lot more that way.
Absolutley !!
A pair of MM on ebay will easily go for £120 - I sold a pair of MM for that within a day or so on ebay a few weeks ago. However, on your guitar, they will not increase the value at all.
Agreed.
Unless the guitar is REALLY cheap (ie the pickups are worth more than the guitar), then replacing the pickups might even reduce the valve of the guitar — this is especially true with vintage guitars. Alternatively you can put your pickups in your new guitar.
Re Denmark St. there are several shops that will pay OK money for guitars. Second hand Les Pauls are relatively easy to sell at the moment and quite hard to find at the right price (probably due to the recent Gibson distribution deal + price increases), so some shops are happy to only make £200-300 on a guitar they can flip quickly. Alternatively you can go for a commission sale which means the shop takes say 20%.
To get the best price on ebay you would need give the option of shipping the guitar. If you do this, be really careful about the packing; mahogany neck guitars are susceptible to neck breaks.
Realistically prices on ebay should be less than those in a shop because you can try the guitar out before you buy in a shop, and you also have legal comeback against misrepresentation by a shop.