It would have been nice to spend time with you tomorrow.
この場合、次のように言えますよ。
ーI wish I could have gone out with you tomorrow.
「明日、あなたと一緒に出かけられたらよかったのに」
I wish I could have ... で「…できたらよかったのに」
ーIt would have been nice to spend time with you tomorrow.
「明日、あなたと一緒に時間を過ごせたらよかったのに」
It would have been nice to ... で「…だとよかったのに」
ご参考まで!