I agree with opting for play value over quantity ... also check out your community for a toy lending program no need to buy when you can borrow to get variety and rotation!

I prefer open ended materials for children specially when working with 'mixed age groups' because than each age group can use them different depending on their age and stage

When choosing toys for the playroom I always try to envision at least 3 different ways the material could be used by children this guarantees they will come up with at least twice that and the material will be a good investment than!

Staples for me are:

A large wooden 'house' which is just stained plain wood to leave it open to the imagination ... serves as doll house, the fire department, the hospital, the farm, Santa's workshop and so forth so no need for me to have to store all those different Fisher Price style units .... one staple piece that can be used for a multitude of different playscapes depending on what accessories are put out with it and the imagination and interest of the children.

A good set of wooden blocks along with organized accessories like cars, trains, planes, community helper style people, little animals and so forth to add to their play here ~ fun for all ages to create things from simple stacking towers to complex playscapes.

Dramatic play centre stocked with real life things like food boxes, pots, pans, dishes, cellphones, scraves, dress up clothes, babies, calculators, cameras and all the other things children will use to 'role play'.

Book nook ... a place for quiet exploration of books, puppets, puzzles and just lounging ... again aside from the staples of perhaps little chairs and what not no need to buy hordes for this area ~ make use of the toy lending library for variety and rotation

Creative Discovery area ... a small table and chairs set up as place to explore open ended craft materials like coloring, painting, gluing and sensory like play dough, science nature or discovery invitations and so forth

Musical instruments ... a collection of materials to use to make music with.

Everything else on my toy shelves are open ended materials .... a collection of different textured fabric peices and scarves, a collection of cellphones, cameras, binoculars, calculators, computer key boards, joy sticks, a collection of 'large lids' which serve as food, money and 'treasures' in their play and also get used for sorting and classification and so forth ... my children will play more with real life 'bits and bobs' collected from around the house and second hand stores than they would with traditional toys like shape sorters and 'themed' Little Tykes or Fischer Price style things ... not that I do not have a few of these types of things but just not my focus for them in the playroom.

Sometimes with children LESS is more because it encourages them to think outside the box and use their imagination in their play ... my children are NEVER bored and some days they will play for hours with just a bin of lids and few other things they collected and their play will evolve from one concept to another as the change what those lids represent for them