I've often heard that spicy foods can speed up your metabolism, I presume, due to the capsaicin. Though I'm sure this is a minor effect - I doubt eating a pound of jalapenos a day will help me lose weight - has the medical/nutrition community quantified how various levels of capcaicin affect the body's metabolism?
Capsaicin do affect your metabolism. It affects your Capsacin receptors ( scientifically TRPV1 receptors). These receptor starts calcium influx into various types of tissues. In endothelial cells because of this it mimics stress response (McCarty et al 2015). Quoting from McCarty et al,
Clinically, ingestion of capsaicin-or its less stable non-pungent analogue capsiate-has been shown to boost metabolic rate modestly. opical application of capsaicin via patch was found to increase exercise time to ischaemic threshold in patients with angina
Coming to your question, there are scientific studies which suggest that capsaicin helps in maintaining weight by limiting weight regain after weight loss. Not just this, capsaicin has also shown potential in treatment of obesity. However you should remember that it will required specific amount of dose (you can check details in papers I cited ) to help maintaining your weight. Do not eat pound of jalapenos a day :P
Scoville scale is used by legislators to specify the allowed concentrations on pepper spray used by the police.
Although that is most important for excessive concentrations, you'll find more studies using this scale in relation to the effects you look for (for instance: https://scholar.google.com.br/scholar?q=Scoville+scale+metabolism).
The Wikipedia article cited talks about "sensation of heat", and indeed we sweat a lot when we eat strong peppers. But I think that eat the maximum diversity of food is healthier than seek the "best foods" according to the "public opinion" of the season. You should be worried about living healthier, not just losing weight. Seek the former and you'll reach the latter.