Well if you look at ALC from LBA, we have:
14 flights a week from Jet2 Boeing 737-300 (Which could also be upgraded to a 757 if needed)
7 flights a week from Jet2 to Murcia Boeing 737-300 (Also could be 757)
1 Thomsonfly 757 a week to ALC, and one Astraeus 737-700 to ALC.
So look at it that way, if LBA can shift roughly 3200 (Could be more if 757 used,) seats, then surely NCL can shift roughly 4200?
And looking at Palma from LBA:
14 flights a week from Jet2 737-300 (Apparantly MAN-PMI will be operated by a 75', so would probably expect a 757 to be used from LBA)
3 flights a week from Thomsonfly 757
1 flight a week from Astraeus 73G, Air Europa 738, Futura 738 and Spanair MD83.
So thats looking at around 3500 seats a week, and thats without a 757 been used with Jet2!
Regional airports really seem to be able to fill the capacity on these sorts of routes.