I have upgraded Vista to windows 7 with an improvement in WEI.
Vista - Window 7
5.9 - 7.1
4.8 - 7.1
2.1 - 5.2
3.2 - 5.9
5.9 - 5.9
Vista and Win7 WEI scores are on different scales no point in comparing. Best used as a tool to see the slowest score for hardware upgrades.
CCleaner will clean every user. It might require running on every login, or installation at admin (run as admin) level.
Anti-malware software? What for? If your system is slow, there is no reason to believe that malware is present. The added software will add to the slower system, if it is 'always on'. Popups, unsolicited network activity and so on would be more symptomatic, but with Windows, there are so many automated and scheduled tasks, that the average user wouldn't recognise malware from a scheduled sync of updates. If there is malware, more likely the system would have slowed noticeably in a short time.
Using CCleaner, go to 'tools' then 'startup' and see the list of processes enabled. I have 6 out of 43 enabled, and one of those is purely aesthetic. I guarantee that a third or more of the processes in that list can be disabled and your CPU and RAM will thank you for it.
There's a 'save to text' option too. If you like, PM me the list, and I'll chase down the worst offenders for you.