For armor, not usually. It does for weapons though. Forging a weapon will cost more zenny and require more/rarer materials than upgrading something you already own into that same weapon. Also if you decide you want a G-rank Black Gavios gunlance for example, you'll first need to forge the base Gravios gunlance with low rank materials before upgrading it with rarer and higher rank materials.Also, does material from low-level monsters help build good gear, or does it become useless at a certain point?