Local teeth whitening business, already doing FB ads, Instagram ads, Adwords, little bit of content marketing on YouTube and will be "scaling" those channels over the coming weeks/months, but wanted to know about offline strategies or where else online I can get the best value for my marketing spend.
I think you are already doing enough for the nature of business you are in. What you might need is a digital social expert to run some analytics on what you have already done to help you understand what is working and what is not, and maybe fine tune your spends.
Without knowing your competitive space it is impossible to recommend a clear communication strategy that will deliver the growth you aspire for.
Commenting generally, once you have generated enough trial, further business growth will be dependent on the quality of service you provide - right from the look and feel of your outlet / clinic, your location, parking, to the quality of dental experts and their service and customer orientation.
The very nature of your business is such that word-of-mouth is the best marketing which you can influence through your service but cannot control totally. Though a small social media nudge can help. After initial trial it is as slow build, unless you either increase locations or buy out competitors.