Blending and matching sprayed on popcorn ceilings is an inexact science and you should not expect a perfect repair, unless you want to re-shoot the ceiling with an air compressor and paint hopper gun. If you do want the ceiling done over, ideally scraping down the old popcorn to an almost flat surface would do the best job. It is possible to spray over the whole area after first repairing and matching the old texture, the best you can. What would most likely be the least costly approach, might be a multiple step process, as explained below.
 There are different problems that arise due to water damage, holes in drywall, remodeling or whatever. If a ceiling or wall has mildew it must be first eliminated, then any seams needing drywall taping must be dealt with. With the area compounded, sanded and primed (one coat is enough), you'll be set to begin. Understanding what painters use when initially spraying a new ceiling helps when it comes to matching the finish. They could use any of the following: Imperial ( fine, medium, course) dry texture additive or a similar product, latex ceiling paint with or without water added, joint compound, leftover primers,or water with very little paint. I'm certain other mixes have been and could be used, but you get the idea. My experience has taught me that having 3-4 different brands of dry texture additive of medium consistency, and adding joint compound, ceiling paint and a little water work best on a typical popcorn ceiling or wall. Now, of course some finishes are fine or sand, others swirl, others were applied with texture already in the can of paint. All these require various thicknesses when mixing, and different methods of application. You may need a regular nap roller cover or even the "loop" roller cover. My usual approach is to use a 3" paint brush to apply the mix. This way you can swirl if needed or add more to a light spot you may miss the first time through. Most of the time 2 coats are needed to get close as well as adding about a cup of joint compound on the second application to hide where the repair meets the old texture. After a 24 hour drying period, a painting of the entire ceiling, for color consistency, makes a big difference. I tried to summarize this a little since there are so many possibilities that could come up.
 One last thing to mention concerns using the acoustic patch spray can. I carry a couple of cans with me but have yet to find a use for the product. If a person was not concerned about how it matches up, I suppose it would be fine in an inconspicuous area. It creates a "cottage cheese" and or popcorn texture look. Maybe it would somewhat match in an area done with the loop roller cover and premixed texture and paint? If it is used it certainly would reduce the amount of labor needed to get the end result. Hope this helps you out!