There is no good resolution here. IMO the best option is using a SSD that can handle the wear leveling tasks without TRIM.
SanDisk, and just about every other maker, will almost certainly not be developing their software for XP or Vista, and much of their technical support staff may not even be able to provide reasonably good service. They may not even be testing their software with those OS’, and you cannot fault them for this given software compatibility development for OS’ that have passed both mainstream and extended support generally means massive investments, limited success, financial loss, potential liability, and modifying software to work better on older operating systems can complicate progressive quality improvement for current OSs. Newer versions of SSD Dashboard may very well play regressively and regressively worse with these OS’ as they are progressively updated to work better with modern OS’. Further, SSD development is rapidly moving away from BIOS, FAT, and Master Boot Records, in favor of modern equivelents that legacy OSs have limited support for. What that all equates to is something most companies don’t want to say outright, but getting good support will be an increasing problem and the individual may wind up having to make a much larger time & monetary investment.
If the user does not want to upgrade to a newer operating system (which there are certainly many reasons to use an older OS), the best they can do is to purchase a SSD that uses a controller known for being able to handle garbage collection without TRIM. XP & Vista and TRIM have never been very good friends. In the case of many of the Micron SSDs using Marvell controllers, the SSDs handle garbage collection both on-the-fly AND especially when the computer saw prolonged downtime…simply configuring the computer to not go to sleep and instead just turn off the display to leave the computer sitting idle for hours allowed the SSD’s controller to handle the garbage collection and keep the speeds running fast. If the only time the computer is powered on is when the SSD is performing reads and writes under normal use, without TRIM, the SSD’s controller may not have the time needed to handle this garbage collection and the speeds will progressively drop.
Another option is physically removing the SSD from the computer, plugging it into a SATA port with power BUT NOT DATA, and letting it sit for 24+ hours will allow the controller to handle cleanup.
With XP, I’ve used CCleaner as a hail mary of simulated manual TRIM using secure delete and it has worked OK. But if you are using a SSD with a Marvell controller, the best solution IMO is allowing it to sit idle as described. SandForce, Samsung, and Silicon Motion controllers, in my experience, do not do this nearly as well. I am not sure about Phison controllers.