First off, it's good to understand the difference between active dry yeast and rapid rise yeast. Active dry yeast is a larger granule of yeast in which the outer shell is composed of mostly dead cells entombing the dormant nougaty goodness inside. It has to be proofed to seperate out all the cells and rehydrate the interior active cells.
Rapid rise yeast is a typically a combination of 2 different strains of yeast (so those with a very discerning palate might be able to tell the difference, I've never really tried). The granules of yeast are smaller and dried slower to preserve more yeast cells. Ascorbic acid is also added to push the yeast into overdrive a little faster.
A great video that helped me a lot is http://how2heroes.com/videos/dessert-and-baked-goods/yeast-101 I have noticed before issues with Rapid Rise yeast not proofing very well the second time around. Apparently it's designed to give you one really good proof and then die out (play hard and die young). Instant yeast however is Rapid Rise yeast without the hardcore party attitude. It's what they use at the King Arthur bakery test kitchen, so that's good enough for me! They say to use them interchangeably, but many other sites I see show a difference of about 20%.
2 Tbsp Active Dry yeast ≈ 1.6 Tbsp Instant Yeast
this is a technique that might help with the shell issue:
I suspect your croissants are losing humidity during proofing, possibly freezing the butter block, and possibly baking resulting in a harder shell. If you have a humidity controlled proofer and oven, then those parts may not be your problem. Otherwise, read on:
Peter Reinhart in The Bread Baker's Apprentice suggests pouring boiling water in a flat pan/container and placing in the bottom of the oven during the baking (of breads) in order to keep up the humidity. This Link has the recipe published with Peter's permission. Notice how the freezer doesn't come into play (freezer is a dehydrator and pretty good at it, too) although some recipes call the freezing part a must.
Croissants are lighter than bread loafs so they may require a different humidity profile than breads during baking (as noted by commenters). However, for proofing humidity levels should be high and the temperature around 80F or 27C.
To achieve that, for the proofing period keep the dough in a turned-off-oven and turn on the oven light a long with a the boiling water method. This usually prevents 'the skin' formation and a dried out crust. It also helps with getting a better rise during baking. The oven light bumps up the temperature but if you're room temperature is close, don't bother.
You may wish to read this piece on humidity and baking and generally the Maillard Reaction. Here's an excerpt that might explain the problem:
"Under dry oven conditions, the dough will have rapid evaporation of the water from
the exposed surface. This will cause premature formation of a dry inelastic outer shell
on the bread surface"
Best Answer
You can add a handful of pumpkin seeds or sunflower seeds. You don't need to adjust any of the other ingredients.
Sunflower seeds contain a ton of good stuff, including fibre, according to Wikipedia:
"In addition to linoleic acid (an essential fatty acid), sunflower seeds are also an excellent source of dietary fiber, some amino acids (especially tryptophan), Vitamin E, B Vitamins (especially vitamin B1 or thiamine, vitamin B5 or pantothenic acid and folate), and minerals such as copper, manganese, potassium, magnesium, iron, phosphorus, selenium, calcium and zinc.[5] Additionally, they are rich in cholesterol-lowering phytosterols."