It definitely is. The LP120, out of the box, already has higher-quality components than the LP60, and those components can be upgraded to still better components (the LP60 does not allow for replacing any components except the stylus, and even then, only with an identical one). It also has several additional features: the ability to play 78 RPM records, speed adjustment (or lock), reverse play, a sync strobe, and (a subtle but useful feature) a cueing lamp. The build quality is also much higher. Of course, the setup is a bit more involved than for the LP60, but this is probably a good thing overall; you end up with a customised ideal setup, rather than a universally “good enough” setup.
While the case for buying the LP120 as a first turntable is clear, it is admittedly less so if replacing an LP60. I would still say it’s worth it, but there are a few notes for the switch. Notably — though the cost is sunk — you’re spending “more” than you would be if it were your initial purchase. Practically, the LP60 does have one feature that the LP120 lacks: automatic cueing and tonearm return. The LP120 assumes you know what you’re doing, whereas the LP60 tries to help you out a bit more. Additionally, the tonearm lowers more slowly than on the LP60. (Again, this is probably a good thing: while it takes some getting used to, it means you’re less likely to damage your records.) Still, I would consider the LP120 an excellent upgrade.