Let's consider a few important points here.
Upgrading libraries does not make your views magically use the new versions right away. And, as Spartacus does not guarantee backwards compatibility, your customizations might rely on functionality that changed in the newer version of Spartacus core which forces you to adapt your code on your own. While there is a mechanism of feature levels and feature flags which should facilitate the use of older minor versions within the same major version, so far we can’t confirm that this mechanism is consequently applied for all features though.
Upgrade is, thus, another project of some (but possibly limited) complexity. If you want to avoid risks in this area, follow our recommendation of reducing the scope of customizations as much as possible.
Upgrade to a new Spartacus version may force you to use a new version of the backend so you might end up in a much larger exercise than initially expected. Maintaining the ability to upgrade forces you to stay current on the SAP Commerce version.
Spartacus is still growing and new features might mime your customizations. Thus, you will face the question whether to stay with your custom or migrate to the standard solution in this particular area. We advocate the use of as much standard as possible as this makes the platform future-proof. It’s fair to expect that the more upgrade-related effort the earlier you jump on the Spartacus train.
On the final positive note - our experience shows that putting up a patch version on a project has proven to be unproblematic in all cases.
If you’re in doubt whether Spartacus is your best or only option, we can help. Our team has 12+ years of experience in working with SAP Hybris. We have a unique knowledge of decomposing frontends and backends for SAP Commerce customers. This includes successful takeover of launched projects that other agencies failed.
We demonstrated the quality of our work in numerous successful projects for customers with revenues of 500M to over 1B EUR where commerce is the key to generating sales. We can help. Drop me a line.