I also owned a Nova150 before moving on to separate components. I agree that with the same loudspeakers, you may not hear a very significant difference in SQ just from a new integrated amp. Tweaking the speaker positions, listening position, and room acoustics are all likely to make bigger differences. Furthermore, in terms of form factor and control features, the Nova 150 actually is quite good.
But if the upgrade bug is really biting you, you might consider moving up the Peachtree line to the Nova 300, or better yet, to their Gan400 amp and PreDac. Through a Peachtree dealer, you may be able to get a fairly generous trade-in on the Nova 150. Some of the pricier Peachtree products use more advanced DAC chips and may also be quieter, compared to the Nova 150. Some of them also offer balanced XLR inputs/outputs. Or, for the price of the Gan400 + PreDac, a dealer may be able to show you alternatives you'd prefer. Maybe Anthem STR or one of the NAD integrated amps that offer built-in room correction and front-panel LCD touch screens.