If you really like your speakers and plan on keeping them for some time, then amp upgrade is definitely a right move. You might want to upgrade speaker cables too in this case. Without knowing your speakers and taste in sound and music, I'll just mention Gryphon and Rowland, to add to your list.
However, you said you'd never upgraded your integrated - maybe you like it.
However, you said you'd never upgraded your integrated - maybe you like it.