I’m not clear from your post if your reservations in place are park reservations or VGC reservations. Throwing out some possibilities that may help if you have VGC reservations -
Unless things have changed, since opening there have been two park reservation buckets, one for Disney hotel guests and the regular one for non-hotel guests. On some dates when the regular buckets had no availability for park reservations, the DLR hotel bucket still had availability. The DLR hotel reservation bucket is open/visible for DVC VGC reservations after you link your DVC reservation on the DLR website.
Unknown here is if Disneyland will have three reservation buckets starting August 25, adding a bucket for Magic Key (MK) holders, similar to what WDW had for AP’s at their reopening.
- Also unknown is if a Magic Key pass can book from the hotel reservation bucket with a confirmed Disney hotel or DVC VGC reservation…we may not know that until folks get MKs and try to book from the hotel reservation bucket.
- So, if you want to chance it, buy your MKs & then look for same day park availability in the hotel park reservation bucket should the MK bucket be fully booked.
- Maybe wait a few days after August 25, so folks can post back on what they are seeing re reservation buckets and ability to use the hotel bucket with MK, to see if any of these are viable options.
Another option might be to purchase a regular multi-day ticket to book park reservations in advance of your visit, then convert the ticket to a MK pass while the ticket is still valid. This would ensure you had park reservations for the desired dates of your stay. From the DLR MK terms & conditions page, under Upgrades -
UPGRADES: A Guest wishing to upgrade to a Pass from another form of eligible Disneyland® Resort theme park admission media must upgrade on the same day in which the original form of theme park admission media is valid, and must choose a Pass of equal or greater value than the retail price of the original theme park admission media when it was purchased. The difference in prices must be paid in full at the time of the upgrade. If an upgrade to a Pass is made from a multi-day ticket, the Pass will be backdated to begin on the first day that such ticket was used; if an upgrade to a Pass is made from a lower level Pass, the new Pass will have the same expiration date as the original Pass. Each guest wishing to upgrade their theme park admission media to a Pass must be present at the time of the upgrade transaction. Fully used, or partially used and expired, theme park admission media, complimentary ticket media, special event ticket media and ticket media stating its ineligibility for an upgrade may not be upgraded to a Pass. Upgrades are subject to Pass availability. Downgrades are not allowed.
You mention possibly paying $10 for parking in Simba to get your MK pass prior to your visit. Not knowing how many ticket booths will be open for upgrades or how long that process might take, it might end up being more than $10 to park in Simba - from DLR website on DTD parking -
The first hour of parking costs $10. Validations apply after the first hour of paid parking.
Enjoy an additional 3 hours of same-day parking with a $20-minimum purchase and validation from any Downtown Disney location—or up to 5 additional hours of same-day parking with validation from any Downtown Disney table-service restaurant.
Beyond these validations, each additional hour costs $14, charged in 30-minute increments, with a minimum $7. The maximum daily parking and lost ticket fee is $66. Parking is subject to capacity.
Another unknown is if an existing future park reservation associated with a ticket will be transferred to the MK pass after an upgrade, or if the ticket reservation will be canceled when the ticket is invalidated with the upgrade & new park reservations are needed using the MK from a MK reservation bucket. You may need to contact Disney for help with this question, or else maybe the CMs in the ticket booths would be able to help. This is a big unknown until folks try this after getting MK upgrades with future park reservations in place.
No-cost parking options just to buy the MK pass would require finding someplace within walking distance where you could park for a bit. I’m sorry, I don’t know Anaheim well enough to be able to suggest a place for you.
Re your question on whether your MK would start if you used the parking perk with the Dream key but could not get a park reservation after purchase - it appears so after reviewing the MK terms & conditions (bold added by me) -
UNACTIVATED PASS EXPIRATION: A Pass is valid for applicable privileges for one (1) year from the date of use of the Pass for first entry into a Disneyland® Resort theme park or use of the parking benefit on the pass for a fully-paid first entry into a pay-on-entry lot at the Disneyland® Resort. Use of a Pass for a discount on parking will not activate the Pass. Pass privileges will not be available until such Pass is activated via park entry or applicable entry into a pay-on-entry lot; provided however, that park reservations, as applicable and subject to associated restrictions, may be made in anticipation of activation of a Pass so long as such Pass has not expired.
Good luck with working it out!
Or I guess I can pay $10 to park at Simba and save a whopping $10 for the key then. Does anyone else have any other ideas that I'm not seeing? At least with WDW we have the opportunity to wait on hold for 4-6hrs to purchase our DVC APs.
And the CM had heard nothing about the DVC $20 discount being applicable for the keys. 
