I disagree. Rather, the use of 'thank you,' standing alone, is inappropriate in this context. It appears distastefully generic and unprofessional, and is likely to be confusing to the recipient as to what, specifically, you are thanking them for.
However, it's perfectly appropriate to include a full 'thank you' sentence immediately before your closing with 'best regards' (i.e. 'thank you in advance for your cooperation,' or 'thank you for your continued professional support.')
Thank you for reading my advice. I look forward to hearing back from you in the near future.