Yes, the output is very small, and because of that, I'm suggesting to use an annalog-digital converter with 24 bits. Let's do a numeric example with PT-100:

Let's suppose I need to measure a range of 100 degrees with a precision of 2 digits, using a resistance of 3.3k on R1 and V1 = 5v:

Resistance at 0 °C = 100 Ω; voltage range on Vout = 147,06 mV

Resistance at 100 °C = 138.5 Ω; voltage range on Vout = 201,40 mV

Calculating the voltage range on Vout = (201,40 - 147,06) = 54,33 mV; precision of 2 digits: 0.01°C = 0,005433 mV, this is the minimum resolution I will need.

Now, using a ADC with 24 bits on 5v, resolution = 5/2^24 = 0,00029 mV

In this example, I will have more resolution than I need, and this is great. There is any problem to read a sensor with this mode?