A few questions:
1- What's your favorite hiding spot?
My closet (for short term hiding.... like "company-will-be-here-in-an-hour" kind of hiding) and basement (for "I-don't-know-what-to-do-with-it-but-I-can't-make-myself-part-with-it-right-now" hiding). But I also have a large finished room (considered the "playroom") over the garage that has sadly become storage for my WW stock (I work for them at a travel location where I do not have a stock room) and for DD's college overflow (she has spent time in dorms, in apartments, and a semester abroad, so she has a wide assortment of stuff that she may or may not need during any given semester!). It isn't tragic because it is out of the way and out of sight and my kids are grown, so no need to "play".... but it has become WAY to easy to not make the decision to part with anything because there always seems to be room to put it somewhere!
2- What do you hide, that you KNOW is useless, but you can NOT seem to give it up & toss it out?
WAAAYYYY too much! Mostly sentimental keepsakes or thinks that have value (or at least perceived value to me) that I haven't bothered to take the time to sell. The list of actual items is much too embarrassing to list here... but I will say we have lived in our house for 22 years now and there are a few items in the junk drawer that have probably been there for the full 22 years!!!!!!!!!! Okay... I'll confess one item..... I have an antique bone-handled 3 tine fork in there..... I have a sentimental attachment to a MEMORY that connects to the fork.....but I can have the MEMORY without the FORK, right???
3- How do you just "let go" of the things that mean so much (kids drawings) but really need to go?
Photographs and scans.... honestly. I don't need EVERY paper that my kiddo colored in preschool.... but maybe the one from the first day and one from the last day.... or a special card they made or the first time they wrote their name by themselves. When my children were attending preschool I DID make the mistake of saving every single solitary paper..... in date order, in binders and boxes. But that just gets to be TOO MUCH! Especially when the projects start to be 3-d...... like the indian tom-tom made from a large coffee can or the Thanksgiving turkey made from paper grocery bags or the Nativity manger made from a clementine box. Time to take a picture (with or without the child) and toss the item (after it has graced your dining room or art gallery for an acceptable amount of time, of course!). I only really keep the truly special pieces of paper .... and they go into the scrapbooks or the small projects (like Christmas ornaments that are easily stored). I scan or photograph the "semi-special" stuff.... and ditch the rest. Unless your child is going to be the next Walt Disney, there will NEVER be a museum in their honor looking for this stuff and you will NOT be doing your child a favor by leaving it for them to deal with after you are gone! (Or foisting it upon them when they move out!!) BTW, this may be easier for me to say now that my children are grown (20 y/o DD and days-away-from-18 y/o DS).
DD did me a favor by doing her very first crayon drawing on her highchair tray instead of on the paper..... so there was no way to save it other than a photograph! And DS did me a favor by writing his name (without help) by himself for the first time on the playroom chalkboard..... again, no way to save it other than a photograph!
I'm really excited about that because like you said "the great shuffle" doesn't allow you to REALLY see what you have...but: when putting it in boxes, HA! Now, THAT is decluttering! 
