Do you own this boat yet or is the 60 foot boat + a 10 foot tug deck (70 feet total) a dream boat? If you have it then stick with it, you can go pretty much anywhere except for a few bits in the north and a couple of levels down south, more than enough for anyone, however, if this is just your dream for the future then consider that most of the comments about what can (with the know how) be done in a 70 foot boat have been made by some of the best and most experienced of the members on this site. Somebody's law says that work expands to the time alotted, likewise junk works on the same principal, you carry baggage you no longer need e.g. beds for friends/children who might come to stay. A lot of the long time liveaboards seem to be happy with their 58/62 feet of space and the ways that makes their lives easier. Do you need a dinnette, a walkabout bathroom with shower and hot tub,sauna and changing rooms?
Anyway how much diesel and water can you store on the tug deck?
If I already owned the boat or it was a bargain I'd go for it but if not then I'd look to the others here who manage to live quite nicely on less length and see how they show size doesn't matter.