filters don't increase receive, they decrease or increase, band width so
that you don't hear or bleed over onto adjacent frequencies more then say
1.9KHZ or 2.3 KHZ away.
If you want to get better performance, check and see if you can find a 6KHZ
filter for USB LSB for the Kenwood 570.
you can legally run 6KHZ wide filters on all HF bands.  The wider filter
will give you increased audio fidelity and will increase the audio quality
of your transmitting station.
I am at a loss to why manufacturers don't put 6KHZ filters as a stock option
in radios.  Something perhaps about reducing adjacent bleed over and
tightening the receiving frequency so you don't have to hear the guy who is
4 or 5 K down from you or up from you all the time.
If you want tighter control over the stations you hear or if you find that
you run into areas of the HF bands that are so crowded that you hear
stations above and below your receiving frequency, then perhaps a narrower
filter then what you have currently might be an option.
As for CW, it is recommended that the narrower the filter you use, the
better you will do.  Like a 500HZ filter will get you very narrow easy to
tune cw signals and the same for those trying to tune and copy your station.
Hope this is an adequate explanation.
Does the TS570 have selectible filters? and if so how many filters can you
have say for USB or LSB?
Conditions and the traffic on the band has alot to do with which filter you
might use at a given point.
For dx you might want to use a narrower filter for the sharper audio, or for
rag chewwing on 80M or 40M you might wanna use a 6KHZ filter so everyone can
listen to a pleasant sounding and full bodied sounding radio.
Also, do you use AM on 80 or ten at all? if you do then a 10 or 15KHZ AM
filter might be handy...that is, if kenwood or other manufacturers even make
them for the 570.
If it was my radio, i would find the widest filter possible for USB/LSB and
the narrowest for CW.  Also the widest possible for AM as well.  Just my
opinion.

Regards
Colin