While that's true, i think crimea and the associated warm water port (sevastopol) is of strategic value. After the crimean invasion, the mainland of ukraine has cut off the water canal, which meant that the peninsular needs to be constantly supported by the russian mainland. It's not quite sustainable in the long term for russia to do that.

The land bridge is their "solution".

I don't see taiwan as similarly strategic to china. It's more politically motivated - that taiwan has turned into a democracy that is pro-west, right on their door step, instead of "returning".

On the other hand, an invasion of taiwan is something that can be used to quell domestic problems...