@Ang ****
if I'm correct, as a general rule you can indeed be asked to provide anything that you originally delivered to obtain a visa, as a double check. It's not a general rule to have it all with you (it's even explicitly NOT required for instance to have proof of onward travel upon entering, despite this being required to get the visa).
I think it's good that IO's warn (but still let you in) when you're at the edge of what they could accept. So this one pretty much said that he'd have gone the other way than the embassy had you requested entry permission to him instead. Not sure that'd be true; it may be a warning to make you aware that abusing tourism-purposed entries isn't gonna hold up forever. If you then get a proper visa instead, he is saving you potential disappointment.
However, from your story, I'm not convinced his warning was entirely justified. Entry stamps shouldn't matter. If you only visit your property but you then immediately return to Singapore each time, where you live, you wouldn't qualify for any other visa anyways (except maybe elite). These visas typically require stuff proving some activity or commitment in Thailand, at least to keep them alive via the yearly extension. Myself I'd qualify for the marriage visa for instance, but I can't keep it alive once I move out. I'll also have to do exempting then, a couple times per year. That shouldn't yield any trouble (I hope :p ).