morav:
I want to use an Arduino to receive data from around 50 different nearby sensors (ideally wirelessly) and send those data to a database/spreadsheet for storage and later analysis.
Let's start at the beginning. How widely spaced are the 50 different sensors? What is area covered? How far apart are the sensors that are closest to each other. A diagram of the sensor layout would be a huge help.
Is it practical to connect several sensors to one Arduino using wires and then have that Arduino send the data onwards by wireless?
As others have said, sensors are usually dumb creatures that must have their data collected and interpreted by a microprocessor. For example you shouldn't think about sending rain gauge pulses by wireless because the wireless may fail to send some pulses due to interference. You should calculate the amount of rain and send that data, and repeat the message if the first one does not get through.
This Simple nRF24L01+ Tutorial may help.
...R