Of course it is valuable, but sometimes the micro companies have not got enough resources for its. Basically they need to check the existing partners (vendors, customers), what they think of them. (quality level of services, quality of products, the way they communicate the partners, and maybe about the leadership). This direct partner can do the best to enhance the reputation, and a lot to damage it. So take care of these key stakeholders.
It definitely is, provided it has a proper context through which it is viewed. For alliances and networking activities, strong reputation is needed to attract partners as per RBT theory.
You might wanna look at family business research, where many firms are small- and medium-sized. Firm reputation also plays a great role in these firms. Here is a paper to start with:
Deephouse, D. L., & Jaskiewicz, P. (2013). Do Family Firms Have Better Reputations Than Non-Family Firms? An Integration of Socioemotional Wealth and Social Identity Theories. Journal of Management Studies, 50(3), 337-360. doi:10.1111/joms.12015