I really really like the Shimano Hollowtech cranks. IMO it's a nice upgrade, but is it worth it? Idk, there are probably better places to upgrade first. Have you done anything with the wheels, tires, saddle, pedals, etc?

Rather than go from a triple to a double, I'd keep the triple and put in a really tight cassette like 11-23, 12-23 or something similar. That will give you smaller steps between gears while retaining a nice low gear if you ever need it.