OK - I decompiled/recompiled the mainRoom PRP. The file is now 40% its original size (!), and after visiting the age, nothing seems to be missing.
Atrion and others: try downloading this version of the ERC Age and see if you still get the long pauses.ERCAge_v4a.zip
Note: I tried decompiling/recompiling the Textures.PRP, but there was no change in size.
Also, for those of you experiencing problems, could you tell me what video cards you have, what the video memory size is, and the driver date? [Use dxdiag to find this out; look on the display tab.]