Your 35mm interpositive is a good source to use for a video transfer and is also an excellent archival record of your film, since it does not get handled except to make a video transfer or an internegative. You might be thinking that if you're going to go all the way for a traditional blow-up you might as well shoot 35mm. There are many factors to consider, however, the actual cost and possible savings really depends on your shooting ratio. For high-shooting ratio films, Super 16 offers you the opportunity to shoot more and save some bucks, which are probably better spent on things in front of the camera rather than inside the camera. Looks like 35mm did 20 years ago.
Film just keeps getting better and better.
To be fair, I have to admit that Super 16 imposes a higher overhead in post. Not in terms of money, but in terms of the knowledge required on the part of the post-production staff. There are many options and variations with Super 16, with 35mm the path is more established and understood. For example, sometimes the reason to shoot Super 16 has to do with the fact that cash is not available at the time of production, but you know it will be there for post. This was my experience with Never Met Picasso, directed by Stephen Kijak and produced by Jennifer Ryan.