By "rendered graphics" you mean "place characters on screen"? If the bottleneck for that is a 9600 baud modem throughput, there's not a lot you need to optimize, even on a 2MHZ CPU.
Also, having programmed more constrained systems decades ago doesn't magically make you knowledgeable on performance on modern hardware with completely different capabilities. In fact, it's probably what causes you to develop a "computers are so fast now, no need to think about performance"-mindset, because everything you want to do could be done in an arbitrarily inefficient way on modern hardware. Performance doesn't matter to you anymore.
Also, having programmed more constrained systems decades ago doesn't magically make you knowledgeable on performance on modern hardware with completely different capabilities. In fact, it's probably what causes you to develop a "computers are so fast now, no need to think about performance"-mindset, because everything you want to do could be done in an arbitrarily inefficient way on modern hardware. Performance doesn't matter to you anymore.