The synthetic cannabinoids like JWH-018, JWH-200, and CP-47,497 are complete receptor agonists, which means they will bind to cannabinoid receptors for life. Once triggered by these synthetic compounds, the receptor is for all intents and purposes dead. You have to wait for the receptor to recycle (the old one to be destroyed and a new one made) before the tolerance is overcome. THC, CBD and CBN are incomplete receptor agonists, which means they bind to the cannabinoid receptor and eventually release, opening the receptor up to be activated again. Tolerance with smoking pot is much shorter for this reason. There is nothing worse you can do for your tolerance than switching to synthetic "spice." With many receptors in the body there is a feedback mechanism to signal that more are required when needed, but this doesn't appear to be the case for cannabinoid receptors, at least CR1 and CR2. They regenerate at a steady rate regardless of how many are functional.
In addition, we don't fully understand the function of endocannabinoids (the ones your body naturally produces to interact with your cannabinoid receptors). These receptors don't just exist for you to get high off weed, they have a function in the body and are activated by cannabinoids that your own body produces to perform some function. Probably (most definitely) as neurotransmitters, although a lot of ongoing research is suggesting they play multiple roles in multiple systems, including blood pressure regulation, immune system recruitment at critical stages in tumor development (i.e. anti-cancer properties), and nerve cell signaling unrelated to nerve impulses (like chemotaxis, or signaling the environment around a nerve cell that there's something it needs, like a hunger signal. Cells have to eat, too). There are at least 2 cannabinoid receptors and possibly as many as 4 additional (with more candidates emerging all the time) distributed through many different tissues and systems in the body, so it makes sense that they would play multiple roles. When you smoke weed you're just borrowing your cannabinoid receptors from their normal function for a little while, THC is not their natural signaling molecule. So you're not only jacking up your tolerance levels, you're cutting off your cannabinoid receptors from performing their natural function as well, which could end up affecting multiple systems in the body.
Synthetic weed is a bad idea for a lot of different reasons, some probably more important than jacking up tolerance.
Cheers.