Of course it all depends on your actual business, income (i.e. how much time can you
afford to spend on internal tools), needs, etc. Since you're talking about client-facing software, I'm going to assume you're in a software development company, which narrows it down a little.
For our company, we don't develop internal tools for any given problem until it's a real pain. You'll know when it's an actual pain (as opposed to just an idea), because you'll keep seeing it crop up in your day-to-day work, and if you talk about it with others on your team, they'll say, "Yeah! I know exactly what you mean, I was thinking about that the other day."
We wait until it's a real pain for a couple reasons:
1) We want to make sure we're not wasting our time; we're mostly engineers, and we all get real, unadulterated enjoyment from building things. It's only too easy for our enjoyment and enthusiasm for building a solution to fool us into thinking there's a problem. But usually, if everyone on the team is instantly excited about the prospect of solving some problem, that's usually a good indicator that it's a real problem.
2) The longer we can put off something, the more information we'll have when we go to solve it. In other words, we give ourselves time to figure out first how we want to work, and then find or build tools around that, rather than trying to fit our system to some tool.
The second reason is really important too, because when we sit down to really think about every facet of a problem, how it affects our work and how we have been putting up with it and working around it, we'll often realize the best solution isn't some new piece of software; it's merely leveraging some tool we already have slightly differently.
For one example, we started losing feedback and updates in email, because some person on the team would get left off the email (e.g. someone hit "reply" instead of "reply-all"), and we wouldn't realize it until some task went un-resolved for several days. We could have built or implemented some sort of support desk system and made it the clients' responsibility to make sure tickets are submitted and then integrated it with email. Or, we could just create a unique email alias for each client, which copies everyone involved. The latter took 2 minutes and improved communication threefold.
If you keep growing, you'll eventually reach a point where anything less than a full-blown software solution just isn't going to cut it. But by that time, you've seen how the team deals with the problem over time, and all the pitfalls of other smaller or less-custom solutions, and you'll be able to build the most awesome solution possible.