Upgrading Mac Mini

Unless you have already "purchased" (downloaded) Mavericks or Yosemite from the Mac App Store, you can no longer update to those versions of OS X. Apple has removed the downloads from the App Store and you cannot buy physical disks. Basically, your stuck with El Cap. (Which is running great on my early 2009 Mini with 8Gb RAM.)

There are other ways of obtaining both versions, however I will not discus it simply because there's no way to guarantee its the official installer and not one someone modified with who knows what.

 

Without further information is impossible to say if a newer OS will help with your problems or not.

What you can do is:

1. If you have original DVD that came with your Mac Mini you can run Apple Hardware test by keeping D pressed when starting you Mac. Once test finishes loading select long test which takes about 10-15 minutes. Does it report any errors?

2. Check your Mac Mini with Disk Utility located in Utilities folder. If it finds errors you have to boot into Recovery mode to fix them (keep Command-R pressed when booting).

3. You can also download EtreCheck which is software that gathers diagnostic information about your Mac: http://www.etresoft.com/etrecheck

Once you have run EtreCheck copy parts of the report that are marked in red, don't post whole report because it is very long!

 

Just to clarify, when you used Disk Utility did you also Verify disk and not just permissions?

You can ignore lines with no signature! they should have no effect in Lion. Only potentially troublesome points are SafariNotificationAgent, com.apple.collabauthd.plist and User Launch Agents which points to MobileMe, Apples former service.

While those EtreCheck results are strange they do not explain why your Mac is slow. Is your hard drive original? If so it might be worn out, you can use utilities such as SMARTreporter to see your drives SMART values. While Disk Utility can check SMART status it will only warn you if drive is about to fail.

Have you tried creating another user account and is the Mac slow when you use other user account? If another account is working normally it's likely there is something wrong in your current account.

 

In that case there are 3 possibilities left:

1. Some software is either incompatible or misbehaving. This seems unlikely because Etrecheck isn't reporting anything. To be safe you should look at Activity Monitor to see if some software is using more processor or RAM than is reasonable...
2. Problem is in the Lion, while its possible I don't think it's likely because OS X shouldn't slow down normally.
3. Problem is in the drive, did you check SMART status? Is there enough free space in the drive? (Absolute minimum is 10%, conventional hard drive will slow down more as it is filled to capacity).

 

I would suggest you upgrade to 10.8.5, at least.

If you want to go further -- say up to Yosemite or El Capitan -- be aware that you probably will want to run these from an SSD, and NOT from an internal HDD (especially on the Mini).

They will run on the Mini (with HDD), but the overall experience may feel more like "walking" than "running" ...

 

Upgrading is the way to go, however, should you be hanging back until you have time to devote to an update, https://fiplab.com/apps/memory-clean-for-mac helped me on a Mini that can't go beyond Lion. Using http://www.opera.com instead of Lion's tired Safari helps too.