Last year the majority of lines were short during
MNSSHP, even at sold out parties but, we have no idea how many tickets are being sold for parties in 2023. More popular rides (e.d. SDMT) will always have a line. I would recommend reading the 2022 MNSSHP thread and 2022?
MVMCP thread but know that those experiences can change in 2023. We won’t really have an answer to your question until the parties start.
I will say though that even at parties very rarely are rides ‘walk-ons’. That sometimes seems to happen at After Hour parties but not always and, those parties are not always offered.
Bottom line is Disney’s popularity has grown exponentially and ‘empty parks’ just don’t exist.