I think you could work on rematches with gym leaders/E4 - their teams get bumps to 60, and get filled out more. Though for the gym leaders, you'll have to get their number and call them to set up the matches:
http://www.serebii.net/heartgoldsoulsilver/gym-rematch.shtml
Oh come on now.
Thanks, so far beaten 3 of the Kanto gyms: Surge (with Meganium), Erika (with Ninetails), and Sabrina (with Gyarados).
Sandslash should beat Blaine, Meganium for Misty, Skarmory for Janine, and Meganium for Brock.