TL;DR at the end
Before RWYS, this made sense balance wise, since every other crop didn't grow in Winter. This is despite the fact that mushrooms don't rot in the world naturally in winter nor do they refuse to pop up in their respective time frames.
Since RWYS was released every veggie has been allowed to grow throughout every season in the game. They are far superior in every sense of the word and have far surpassed the more advanced (requires alchemy engine) and more expensive (even Wormwood has to pay hp for them) mushroom farms.
The meat of my argument
Mushroom farms have fallen behind in a few ways:
Only Wormwood can fully benefit from every single red mushroom for a total of 75 hunger. However Wormwood and every other character can grow pumpkins throughout winter for a far greater 37 hunger per pumpkin. So even Wormwood can grow pumpkins while his mushrooms are sad and rotten. Outside of Winter equally strong veggies exist such as dragonfruit.
For Wormwood it is far easier to plant carrots straight into the ground for the same 12.5 hunger per mushroom 3/4 of the year minus the upkeep, health penalty, spore requirement for highest yield, and winter rot.
Potatoes replace the 20 hp health that blue mushroom brought to the table.
Sanity is a bit harder to replace but you still have melon popsicles and pumpkin cookies (off the top of my head)
TL;DR: There are cheeper and better alternatives (RWYS) for what mushroom planters once offered, this includes even for Wormwood.
Allow them to function even in winter. This can already be done by placing them below ground so all it would do is remove the loading screen.
Final thoughts:
I would be very pleasantly surprised if they could be buffed in other forms too. Such as increasing the number of possible harvest before needing a living log. I will leave that up to the devs.