Deciding between 21 day pass and 2 5 day JR east passes

Hi there,

I've more or less worked out my itinerary for my trip to Japan and I'm trying to work out which pass would be best for me to get. Part of me is thinking I should get 2 JR east 5 day passes to use on the "expensive" days and just use Suica for the rest, the other part of me is thinking maybe a full 21 day pass is best just in case I want to do some last minute side trips or something on days when I'm in Tokyo.

I suppose I'm just after some advice/thoughts- if you think the "savings" of getting the 2 east passes + using suica won't be much compared to getting a full pass, then I'd rather just get the full 21 day pass and be done with it. Getting low on time and I guess I just need to decide bit it's hard to know what's best.

My current itinerary is as follows (I've got some other options for potential day trips depending on how I feel towards the end of the trip but these are the "for certain" things) -

April 4 - 11 - Tokyo with day trips to Kamakura & Nikko

April 11 - 13 - Nyuto Onsen with day trip to Kakunodate (or something else, but definitely a day trip in there)

April 13 - 16 - Sendai with day trips to Shiroishizao, Yamagata/Yamadera

April 16 - 17 - Onsen (Aizu or the one near Bandai Atami - waiting on a response by email to decide) Day trip to Hanamiyama if I go to the one near Bandai Atami

April 17 - 23 - Tokyo with day trips to Hakone and Mt. Takao

Now depending on weather and sakura etc. and if some miracle happens and wisteria come early (no chance haha) then I might consider another day trip to somewhere like Ashikaga Flower Park or something but that's a real "maybe" at this point.

I've used Hyperdia to work out the cost of the travel between the above spots and I'm still not much closer to working out which pass is best- by my reckoning if I estimated about 1000 yen travel on the "non-pass days" (days around Tokyo most likely) is does work out slightly cheaper to get the 2 5 day east passes, but it doesn't give wiggle room for extra day trips.

Any thoughts would be appreciated. I don't want to be pinching pennies and do sort of just want to do what is easiest (within reason) but don't want to foolishly buy a 21 day pass if it's definitely not going to be value for money