I think these are some excellent points, but as far as I can tell the advantages you mention likely only exist in an ideal (possibly theoretical) surgical internship.
My experience is certainly more limited than yours, but from working with surgery prelims (on our PGY1 gen surg rotation) as well as speaking with surgical interns I know at/from med school -- as well as my own surgery rotation during intern year -- i can tell you there is little to no time for procedures as you spend nearly all of your time managing surgery patients on the floor. The OR time/procedures that are available are generally reserved to senior surgery residents then categorical surgery interns (as they should be... it's their field). As for IR procedures, I suppose if you (a). have the time (unlikely) and (b). there are no radiology fellows and/or IR fellows around, you could assist the interventionalist, but these opportunities would likely be few and far between. Furthermore, there's no reason your colleagues wouldn't let you do this as a TY/medicine prelim also interested in IR. For example, I put in more central lines during our ICU rotation than one of the surgery prelims I worked with had all year (zero). This wasn't b/c I had to either, as many of my co-interns did no procedures, it was b/c I wanted to and had the time.
As Smurfette mentions, your actual internship is institution dependent, but I just can't imagine any prelim surgery program that offers enough of these opportunities to offset the significant cost of doing this year over a TY, at least in my mind. Also, you can use your elective time during a TY to do a rads or IR rotation at an ACGME accredited program, which obviously would be the most beneficial.