i just call them as soon as i can, if they don't leave a number i delete.
trouble with that reply is like on here mike, sometimes the written word can be taken the opposite way to how it was intended. and also not everyone has a sense of humour.
i get a lot that just say "how much for cleaning", so i take it that they don't want to write all the measurements down, they just want me to get in touch, you'll be amazed how true that is and ive had many a good and well paid job from them.
but like all email enquiries, some you win and some you lose, but initially i take every enquiry seriously, i have too! its my job, my life, my livelyhood.
thats just the way i do things, not knocking your way, in fact if i was fully booked all the time like you, i may be tempted to go along the same lines. heres hoping.