If you have only match at 37 markers, it is not extremely likely that you will get more matches by upgrading to 67 markers. However, upgrades will sometimes reveal new matches or even eliminate some of your 37 marker matches.
So you may be in situation where you need to "build your YSTR cluster." This would require testing different sons or grandsons of your oldest proven ancestors (only if born before 1800). Also, if you suspect another line could be related to your line, encourage or sponsor that test would be another good option. However, 67 markers is the "gold" standard (both quality and cost) start this process.
Here are some major advantages of 67 markers: 1) Your 67 markers can be analyzed by many haplogroup admins and your haplogroup (1,500 to 2,500 years old) can be predicted. This would save testing costs and would allow you to directly test the most recent SNP pack test. Since this is an Irish forum, around 75 % of Irish are R-L21 and my R-L21 predictor tool predicts 50 % of R-L21 testers, you may have the luck of the Irish and may get predicted to a more recent YSNP than FTDNA's prediction:
http://www.rcasey.net/DNA/R-L21_SNP_Predictor_Intro.html2) 67 markers is really required to chart the connections between testers. Under R-L226 (I am one of the admins for this project), I have charted 80 % of this Dal Cais haplogroup. The above predictor tool will predict L226 with 100 % accuracy to date after several thousand tests. So if you are predicted L226, you have a 80 % chance of getting charted as shown in this massive chart that charts 80 % of the currently known 520 67 marker L226 testers:
http://www.rcasey.net/DNA/R_L226/Haplotrees/L226_Home.pdfI always recommend testing to 67 markers prior to any YSNP testing. Also, I rarely recommend upgrading to 111 markers unless under very special scenarios. The L226 SNP pack was recently designed by FTDNA and is very leading edge. During the last two years thanks to 65 Big Y tests under L226, we have grown to only knowing about L226 to discovering 44 branches under L226. We are adding one new branch every one or two weeks in a very consistent manner. One third of these branches are now genealogical in nature as they are dominated by one surname.
If you have ties to Munster, Ireland, L226 is the only known YSNP branch that is 90 % Irish and 80 % origins in Munster, Ireland. L226 is extremely dominated by Dal Cais surnames. Most of YSNP branches are named DCXXX in honor of our Dal Cais origins. Here is link to my L226 web site and the Irish Type III (L226) web site:
http://www.rcasey.net/DNA/R_L226/R_L226_Private.htmlhttp://www.irishtype3dna.org/index.phpIf you are a Casey with ties to Munster, Ireland, I am also sponsoring a 37 marker test.