The short answer is yes, they are worth it. The long answer would depend on whether or not you enjoyed a little DIY. You can certainly make your own rock excavation kit with a little plaster of Paris, a box and some rocks to embed in the plaster. If you are not a do-it-yourselfer then these kits from Rainbow Resource are perfect.
This one was especially nice because the block is shaped like a piece of land with ‘mountains’ and layers of rock to indicate where you might find the different types of rocks: metamorphic, igneous and sedimentary.

My nine-year-old really enjoyed this kit. It took him about two hours to complete. He did pull out some of our excavation tools from previous excavation kits, and he also cut small squares and numbered them as he discovered rocks. The samples were a very nice assortment of unpolished rocks.

Duration: 2 hours
cost: $15
Level: ages 7-12
Subject area: geology and archaeology