Coming out of orcs, I liked the weeping willows because they offered a lot of culture which had wilted in orcs. They also didn't have a lot of the newer mana event buildings back then, so fewer choices.
The MH tech requiring mana for the upgrade comes in the middle of the Woodelves tech tree, so mana will have been available for a long time before then. Looking at your Winyandor city (if that's the correct one), it looks like you are still in orcs or just starting Woodelves. There are 5 required techs that require mana plus the MH one before you can upgrade it, so plenty of time before it's a worry.