2.4 - I'm not a mechanic and don't know about wages, etc. I've been in my field (plastics engineering) for about 28 years now, 30 years total in the plastics field. I started out "entry level" and moved on from there.
As I entered my second year in the engineering department I was asking for more money. My manager explained that I'd received almost 20% pay increase since moving up from the production floor. I told him "Give me 20% of what you're making as my increase and I'll be happy. Don't get me wrong, 20% of what I was making is nice, but not as nice as 20% of what you make."
The ultimate advice I'd give anyone is that if you don't ask, you won't receive. Be respectful and be ready to back up your request with a list of accomplishments and reasons why you are worth it.
I've worked in multi-operation corporations and now work in a small family owned business which takes good care of me. However, over the years I've been able to bring on skills that cover nearly every aspect of the business. I can handle product design (3D CAD), tool design, tooling repair, plant efficiency improvments, plant layout and development, computer system maintenance and repair, ERP system setup and maintenance, process costing, cost estimating, machine troubleshooting and repair and have even negotiated business contracts. The owners know that if needed, I can do pretty much anything that needs to be done.
I'd compare it to the certifications you mentioned. I'm sure there are many operations that use them as "feathers" in their caps, but I have to believe that being as versatile as possible is respected and rewarded by operations also. I've tried to drill that into my son's head - the more you know the less you'll lose out on or end up paying someone else for. He was in a large corporate retail setting and realized that going the extra mile was appreciated by his manager, but there was little that manager could do in terms of his compensation and/or position. Now he's at a privately held tool and die shop that isn't that strong in benefits, but he can write his own pay check through over time. He's catching on, even leaving earlier in the morning than I do, and understands that the more he can do, the more value he has, and his pay rate will change accordingly.
So, once again, it never hurts to ask and put the best foot forward!
2007 2.4L N/A. Stock + some pretty crap.