As others have said, redosing won't boost the intensity of the peak much, just the duration and body high for the most part. If you want to get the most intensity out of it, take a larger amount up front. If you want a longer, less intense trip, space them out. I wouldn't wait until you're already coming down to take the second dose, as it may not be enough to boost you back to anywhere fun. I would redose within an hour or two of peaking or not at all, but it's up to you of course.
If you've never snorted a 2C before, I DO NOT recommend it. It hurts like fuck. Seriously, people who think MDMA or pharmaceuticals are painful to snort have clearly never tried snorting a 2C. It's not just that it feels rough on the nose; it feels like some awful chemical burn, which continues to burn down your throat with the drip. I've only tried it with 2CE personally but from what I hear 2CI is just as bad. When I snorted 2CE, I spent the first 20 minutes or so totally distracted by the intense pain, then vomited forcefully for a solid 5-10 minutes. It wasn't until an hour and a half or so after snorting it that the pain and discomfort subsided enough for me to start enjoying myself.
In my experience, if you can handle the increased stimulation, higher doses of 2CI are a lot of fun. The headspace seems more properly psychedelic at 30+mg, and the visual intensity keeps ramping up as high as I've been willing to push the doses (around 40).