Hello,
I use the nRF24l01+ radios too. For my nodes I just use the cheap $1 versions (same as you) but for the the main base station I use a version with PA/LNA + ext ant(~2dBi).
http://www.aliexpress.com/item/Free-Shipping-nRF24L01-PA-LNA-wireless-communication-modules-with-antenna-2-4GHz-2Mbps-1000m/709420583.html
about $8 each.
As the higher powered modules use more power I only use them on the base station and not on the battery powered nodes, This works fine for me out of box giving range of over 30m with 3 brick walls and a stainless steel kitchen between.
One little problem with the module is that it has a SMA connector not a RP-SMA connector but it is not too hard to get an adapter for or replace it.
Most 802.11BGN(WiFi) antennas are RP-SMA and because 802.11BGN is also 2.4Ghz you can use Wifi antennas to boost your range, on one of my modules I replaced the ~2dBi pigtail antenna with a cheap 12dBi wifi antenna( the smaller antenna worked just fine I just did this because I could)
To boost your range you can also change you data rate. I use 2Mb as battery is more important then range for me currently but if you drop your range down to 250Kb you should get much better range(~30m) just using the cheap modules. The RF24 library also lets you adjust the transmit power, make sure you have it set to max.