I agree with the OP, Tramadol is a very effective drug, not so much for pain relief, but due to it's other properties on serotonin and noradrenaline.
As someone who has taken Tramadol for years off and on, I think the risk of addiction and tolerance is fairly low if you keep the dose at < 50mg daily. There's a common misconception that Tramadol is comparable to codeine and other true opiate drugs, with a similar drug-dependency risk. This hasn't been the case at all for me, and I can say that Tramadol is nothing like true opiate drugs.
Tramadol is actually an interesting drug though. The opiate-style pain-relief it gives seems to be very pronounced and effective in opiate-naive people for very short term use, but quickly becomes less effective as an analgesic for chronic pain, with daily usage. Increasing the dose in my experience does not improve it.
If you suffer with depression and/or chronic fatigue syndrome (CFS), Tramadol can be a miracle drug when used off-label for these illnesses. I went from being unable to hardly move, experiencing extreme lethargy, muscle/joint aches, mental fogginess etc, to being able to exercise daily (running 4km, lifting weights), and basically leading a very active and productive life on Tramadol without ever needing to increase the dose over 50mg once daily.
However GP's will not normally prescribe it for off-label uses like this, due to other drugs being available and the fear of tolerance and dependency. Even though these risks are minimal in patients properly supervised with no history of addiction or drug abuse.
It's not all good though. There are some significant risks and side effects with Tramadol. Even at low doses (50-100mg). Rapid and severe weight loss is one problem which is a particular concern for people already underweight or who don't eat properly, since Tramadol suppresses appetite and/or seems to speed up metabolism. Another problem is insomnia and disrupted sleep cycles, which can develop in people with no history of insomnia. This can lead to stress, anxiety and cognitive impairment over time.
I think perhaps these side effects (and there's a very long list of other possible side effects besides these two I've mentioned and experienced myself) is what puts GP's off using Tramadol for off-label uses.