Quite honestly, "basic car mechanics" won't help you at all when it comes to something like an Omega V6. Or, for that matter, any car made in in the last 20 years.
I used to do all my maintenance and repairs 40 years ago. Now, when I lift up the bonnet, I can't even name most of the parts I'm looking at. A couple of years back, when the car just stopped and I had to call the AA, the bloke who came along said that if it wasn't something obvious, he didn't stand a chance of identifying the problem, and even if he could identify it, he probably wouldn't be able to fix it.
So much of the modern car depends on electronics that it just isn't possible for the ordinary man in the street to do very much as he doesn't have access to £30,000 worth of diagnostic equipment.
The wizards you encounter on OOF are exceptions, and it will take many years of dedicated toil to achieve their level of expertise.
However, there is a price to pay for this! I won't go into details, as I wish to remain a member of the forum.
I used to think the same J, and had "stopped" doing any work on cars from the time I got the Granada Scorpio, in the same belief as you. That continued through to the old omega - the blue one - which developed a problem that the "dealers" said was extremely rare and would cost over £1000 to fix, "and to the complexity of the electronics this might not be the full solution". At the time I did not have £1000 to chuck at a "possible" fix, so in desperation I started to search on t'web. I found here with an exact description of the fault and the fix, and the information that it was relatively common knowledge - ABS ECU. Armed with that knowledge, and some help from forum members, the ECU was removed, sent for repair, and replaced, in less than a week, for less than £150. Since that point neither car has been to a garage except for WIM - geometry - and MOT's. I have learned, and been instructed, by forum members all the way through, or folks like Elite Pete, Daz, or Chris Gixer have done the work for me, the first time, but have taught me how to do the job should it need repeating.
I accept there are some jobs I'll probably never attempt, but I can now do one hell of a lot more than I could, and I can certainly do all the "routine" stuff without hesitation, and I'm more confident in attempting other work, knowing there is a wealth of support at the end of the phone line .. either by calling or by broadband !!
There are 2 major advantages to that ..
1 . Cost
2. I know the job has been done properly.
Just my views .. nowt else ..