I fail to see why one's income should be of any concern to the Thai authorities - it's not as if they're going to be doling benefits and free health care out to you should you become penniless - they'd just let you starve or die, or both (but they'd do it with a smile)
Basically an ex-pat farang is a one-way Income stream for Thailand - they should embrace that, rather than make it awkward to comply with pointless regulation