What do you suggest? Here are my stats: 2.53 Ghz Intel Core 2 Duo with 4 GB 1067 mHz DDR3
I believe I have only ever replaced the battery 1 or 2 times, hard drive back, screen, and keyboard unibody. I don't think I have actually upgraded anything, though I did ask a local macintosh repair shop to see how much they would charge to tune it up. They said about $200.
As
@Certificate of Excellence said:
Better upgrade to an SSD and max-out RAM to 8GB first before spending money on an M1.
My daily driver and favorite machine is a 17" early-2008 2,5GHz MBP with 6GB DDR2-RAM and 1TB SSD-drive.
An SSD and more RAM makes your MBP fly again.
Replacement of SSD and RAM is a snap following the
guidance on iFixit.
To swap the hard drive for an SSD get an SSD(
50€/500GB), an external USB3-case (
9€) and a clone-copy-App like
SuperDuper! or
CarbonCopyCloner. SuperDuper! is easier to use - CCC has more options.
First attach the SDD (within the external USB-case) to your MBP and clone your internal drive to the SSD.
Then replace your internal HDD with the SSD following the steps on iFixit (make sure to disconnect the internal battery and ground yourself before replacing the drive e.g. by simultaneously touching the MBP-case and a lamp or a heater)
Your old HDD (within the USB-case) may afterwards serve as your future backup-drive for clone-copies.
There are a few more tricks (clone the Recover-Partition for supported OSX up to ElCapitan, or upgrade to officially unsupported versions of macOS with
@dosdude1 's
Sierra/HighSierra/MojavePatches), but that definitely is step 2 and also easy done with some guidance ...