Ocaasionally freezes and opening apps in launch pad is too slow

System: Macbook pro 13" Mid 2012 2.9GHz i7.

Graphics: Intel HD graphics 4000

opening Launchpad is too slow but over all machine runs fine when I use lightroom/photoshop.

Booting time also increased - O/S is on SSD and all apps are installed on SSD.

Occasionally system freezes. Need to hard boot.

Took it to genius bar and they suggested that most probably motherboard is gone and they said it costs around $450

Is there any way it can be quick fixed without changing mother board and if need, is this something doable.

Also, is it really worth it? Genius bar guy is telling to live with it and instead spend money on new laptop...

System is modified almost 3yrs back to SSD and HDD (removed optical drive)

Last year upgraded SSD to 1TB.