I'd look at it from the point of view of the companies who might buy you out in x years time. They either want to do one of two things:
- Remove you from the market because they are losing too many customers to you.
- Add your product to theirs because you add useful features, you have higher growth and you open up new markets for them.
(1) is quite a negative way to approach it and companies often just try to increase their competition rather than buy you out. That said if you bring them a lot of useful customers paying annual maintenance, that helps.
(2) tends to be the better route to go down. Think about what extensions to their current markets there are. They should be niche currently, but you should target those that should grow into useful market volumes. Look by vertical domains (specific industry extensions to the ERP), by countries, by business size, etc.
One thing to remember with either exit is that they will need to integrate your technology and customers with their technology. Think about this from the start. What technologies do your selected companies use? Are you able to integrate with their storage formats, including import/export?
Import is critical for grabbing customers from them, export is critical for a buy-out, it gives that company an easy way to bring your customers over. Think about a very clear XML storage format and use standards wherever possible.