I agree with you that the requests for "lower than your hammer" tier are bad BECAUSE they do not accept "better" material --- it really requires you to have all heads of all materials at day 15 or you will not make it and, as you said, you will lose progress traction because you have to invest way more money into things that might never be requested again.
However, being prepared yields up to 20 customers a day so ... if you keep up with it, I'd say, you still are able to advance the fastest and maybe even faster than fast people that prepare on the fly.
Yeah I found this game through jack :) and since then I love it xD