Acid base issues can pose both acute and chronic problems. An acute problem could arise after one has put say vinegar on a salad and ends up with canker sores. Now, whether that one bolus of acid poses a problem is dependant upon the net acid/base load of the diet. Acutely one can see sleep disturbance and lethargy (this happens within hours and/or days) and chronically one may see bone demineralization and muscle wasting (months and years).
If one is consuming plenty of fruits and veggies and not going overboard with things like salt and vinegar, the long term should be fine.