Well it is up to you of course. As a PIC user from wayback, there is no way I would return those processors with what the Arduino ecosystem offers now.
I have used the Oregon Scientific (Chinese BTW) sensors and think they are quite good quality for the money. My GIT-Hub pages outline two types of project. One is to build an Arduino Uno base station that intercepts OS sensor signals and allows you complete freedom to build your own system from there on. The main trick provided in the code is how to intercept the 433MHz signals and decode them. My strategy was to turn these signals into a string and simply send a serial message across the Arduino's USB/Serial connection back to the main computer (it is now a RPi3, but was an Intel Atom previously). Again this string can be interpreted by Python programs and processed to your hearts content.
433Mhz interceptor: GitHub - robwlakes/ArduinoWeatherOS: Arduino Uno, 433MhzRx and OS WMR86 Weather Station
It also has a good run down on Manchester protocol, which many weather stations use in one way or another, if you wanted to try to roll your own Arduino or PIC version.
The second project involves making your own sensors that can integrate into the OS system without too much hacking. In essence it is designing your own OS sensor (I have one one monitoring solar energy at the moment, and previously had one monitoring lightning strikes). All I had to do was extend the code for the list in the Interceptor to detect the new sensors, and add that to the exported string.
Roll your own OS: GitHub - robwlakes/Weather-Station-OS-Sensors: Weather Sensors, Tx & Rx for Arduino plus 433MHz
Note it easy to create a wireless Temperature sensor from Arduino bits and (as shown in the example given) much cheaper as well, if you have the bits lying around. However it is much harder to replace the OS temperature sensor where low power consumption and long battery life is important. The OS sensors are very battery efficient and getting a home built sensor into this range is certainly a higher level of difficulty.
The Solar Power sensor I made is based on an Arduino Mini-Pro (the only low power alteration is the power LED has been removed) and it survives long term as it uses a solar panel (and why not? 
) to charge a LiPo battery. If your sensor points are near permanent power, then this will not be a worry.
Get some Arduino Mini-Pro boards, some 433MHz Tx boards and some DS18S20 for the sensors, and an Arduino Uno and 433MHz Rx for the base station and get into it.
The Arduino system does not need a dedicated programmer board, usually just a stock USB cable. And you get the IDE free with a multitude of very handy libraries.
Cheers, Rob