I've got a DG4102 and several other AWGs with much bigger memory, and I've got to say that available waveform memory was never a constraint to me on any of those. I've got to admit that I rarely use arbitrary waveforms of my own. Those big memories should in theory permit to store complete audio samples or even short video sequences (ancient composite PAL / SECAM / NTSC format if anybody still uses or needs them). That is, one will find a software tool to somehow convert them into the native file format to upload into the generator.
TBH, I think the DG4000 series is a rather dated design and I would only consider it if it available at a real steal... And if I really need the connectivity and arbitration methods it offers, with separate SYNC outputs and TRIGGER / MODULATION inputs for each channel (other instruments -- Siglent -- just offer a single BNC for all these functions for BOTH channels, so you've got to choose and often certain setups just won't be possible) and a really decent frequency counter function. On the other hand, the DG4000 series doesn't feature "seamless" parameter change in some waveforms, which means the output (Pulse mode for example) will hickup for a few milliseconds if you change the pulse duration and likewise for other waveforms.
Before you buy an instrument, please look at the manuals and consider what features are most important for you. I'ld put waveform memory close to the last place of features affecting my choice. That's basically how I ended up with a total of three (four if I count the now half-way defunct "el cheapo" Hantek HDG2000) AWGs. And still I didn't find the "one for all jobs" instrument...
Cheers,
Thomas