It depends on what you’re trying to fix/achieve… You don’t give us enough information. What’s the problem with the original recordings? How do you want to improve them?
I don’t think hard limiter is what you want… My guess is that you’re probably looking for dynamic compression. There’s a “compressor” effect in audacity. If that’s what you’re looking for you might want to have a look at chris compressor, which is available as a plugin for audacity.
The hard limiter will be introducing distortion on peaks that are above -5.5db.
The result of what you are doing will certainly be “louder”, but probably not “better quality”. As bgravato wrote, it depends what you are after.
If you want to increase the overall loudness then you should use dynamic compression. You can either use the audacity’s built-in compressor or download chris’ compressor: http://pdf23ds.net/software/dynamic-compressor/
If you search this forum for dynamic compression or compressor you should find a lot of threads about the subject.
You might also give a try at steve’s recent equal-loudness plugin: https://forum.audacityteam.org/t/equal-loudness-normalizing/19112/1
Quality is subjective… Depends what you’re referring to…
In your case dynamic compression is not useful. Dynamic compression is used when you have very quiet parts and very loud parts and you want to reduce the gap (in volume) between the quieter parts and louder parts. So dynamic compression will make quieter parts louder and louder parts quieter.
Quiet or loud parts have nothing to do with the type of audio you have, doesn’t make a distinction between what is noise and what is voice.
So if you have a recording were you have a quiet voice over a loud noise, dynamic compression won’t make the noise quieter and the voice louder… If you could do that you would be a very rich man 
Computers don’t distinguish between noise and voice. So when you amplify and audio signal you will amplify both the noise and the valid audio. So amplifying or using dynamic compression on a recording won’t reduce the noise in it while improving the non-noise part of it.
In your case what you can do is to use filters/equalization or noise removal tools. You can filter out certain frequencies. If your recording has only voice, then you know voice only produce frequencies in a certain interval, so you can remove low and high frequencies.
You can also use the noise removal effect in audacity.
On this wiki topic you have some more info about noise removal: Missing features - Audacity Support
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