I suggest that you stop running any registry cleaner on your system.
Such routinely remove entries which the developer determined was unnecessary...being mindful that no program developer could have had any inkling as to what programs and data files were installed on your system. Thus, the criteria used by any registry cleaner...is totally arbitrary and I would consider it great luck if all entries deemed removeable...actually turned out to be such.
Bleeping Computer DOES NOT recommend the use of registry cleaners/optimizers for several reasons:
Registry cleaners are extremely powerful applications that can damage the registry by using aggressive cleaning routines and cause your computer to become unbootable.
The registry is a vulnerable subsystem, in that relatively small changes done incorrectly can render the system inoperable. For a more detailed explanation, read Understanding The Registry.
1. Not all registry cleaners are created equal. There are a number of them available but they do not all work entirely the same way. Each vendor uses different criteria as to what constitutes a "bad entry".
2. Not all registry cleaners create a backup of the registry before making changes. A backup of the registry is essential BEFORE making any changes to the registry.
3. Improperly removing registry entries can hamper malware disinfection and make the removal process more difficult if your computer becomes infected. For example, removing malware related registry entries before the infection is properly identified can contribute to system instability and even make the malware undetectable to removal tools.
Should I Use A Registry Cleaner - http://aumha.net/viewtopic.php?t=28099
Why I donít use registry cleaners - http://www.edbott.com/weblog/?p=643
The usefulness of cleaning the registry is highly overrated and can be dangerous. In most cases, using a cleaner to remove obsolete, invalid, and erroneous entries does not affect system performance but it can result in "unpredictable results".
Unless you have a particular problem that requires a registry edit to correct it, I would suggest you leave the registry alone.
I suggest that you take a look at items marked as Error under Type...in Event Viewer, in an effort to see what the system thinks merits user attention.
How To Use Event Viewer - http://www.bleepingcomputer.com/forums/t/40108/how-to-use-event-viewer/
If I had 1GB of RAM installed...and had what I perceived as "performance issues", I think I'd double my RAM installed, in addition to some of the other steps you have taken.