Don't know about break-in on these, but maybe try losing the cap in order to see if there is an immediate change in the depth of the soundstage?
I have made the tape IC's before, but used smaller gauge solid core wire (26 & 30). I did not use a cap and I did not use heavy gold plated RCA's. I used the Radio Shack RCA's that come 8 to a pack for $2.99, polished up the contact surfaces and then cleaned them with alcohal (these RCA's have very low metal mass). In my setup soundstaging (of these IC's) was not a problem.
If you want an even larger stage (filling the whole room and beyond) then switch to a high % of air surround (oversized 3/8" tubing). Imaging will suffer with the "air" design, but I have never heard a more open sounding cable.
If the "air" surround is too much of a good thing then run a split down the tube in order to reinsert the wire once it has been dressed with Teflon balls/supports. Thread the wire through balls of Teflon (roll Teflon plumber's tape into balls and then punch a hole through the center with a sharp needle). The spacing and number of these Teflon supports will effect the sound (more will close in the sound while sharpeneing up images) and through trial and error you will be able to balance this out to your liking. I would start by using them every 3"-6" depending on the length of the cable. I would also use smaller (than 20 gauge) wire. Once you find a suitable balance mummy wrap the outside of the "split" tube with more Teflon plumber's tape and tie it off at the end. The supports probably alter the sound by adding damping and/or by altering the dialectc properties of the surround (who knows), but they work. In the end you can end up with a hidious looking, though great sounding IC for under $15.