The old Infiniti media may not have 'aged' as well as other, better brands do, (like MCC 004 Verbs), and it's all down to the quality of the dye (or lack of it). I can't see why you think your burner is about to die, try some decent discs first, or if you wanna go cheap get a different batch of the CMCs (just in case it was a faulty lot).
The LG is a good drive, but it can't perform quality scanning. If you frequently burn budget media I'd grab a DW1650 while they're still around (they won't be for long so hurry!). Self-learning technology like SolidBurn is a must for cheaper media so I'd go for either a BenQ 1650/1655 (or equivalent Philips models which you can crossflash to BenQ firmware if you wish to do so), or one of the new Lite-On drives which feature similar self-learning technology. Don't worry about x18 speed, in my opinion it's just a gimmick, I always use x12 maximum as it's the best compromise between quality and burning time.