I agree that most websites have that refresh issue.
I have a definite reason why I want to avoid a complete refresh. Most of my clients are fairly new or have limited inexperience with the website. it's possible that some people will see a total refresh as if they were going to a different website, being hijacked, and be very uncomfortable. sometimes it is nothing more than someone planting a seed to make people nervous. I know this seems a bit over the top, but I have had problems with this.
I see your concern for I-frame and from what I have read since your comment I plan on shying away.
But the fear most programmers have regarding frames is something I don't understand. Is it that some browsers do not support them. The only browsers. I'm concerned with are the ones within the last one or two years. and mostly chrome and Internet Explore. Most of my clients stay within the basics.
needs to be updated to frames (possibly)